ALLEN'S 

HIM  AN  ANATOMY 


SECTION  I. 


HISTOLOGY. 


^WiJ^.llt^Sfc*  tS^**$EFSk  <{Cff^l» 


S;*<3^' 


™  .    *r^SL5L^-A»w  .  \i    ^!V^! 


FROM  THE  LIBRARY  OF 
FRANK  BRANSON  PETRIE,  M.D 


v,  :,:•••• 


A    SYSTEM    OF 


HUMAN    ANATOMY. 


INCLUDING    ITS 


MEDICAL    AND    SURGICAL    RELATIONS 


p.v 


HARRISON    ALLEN,    M.  D., 

I'K'il  ].>~MK     OF     PHYSIOLOGY     IN     THE    TSlVERSITY     OF     PENNSYLVANIA,     ETC.,     ETC. 

ILLUSTRATED   WITH   THREE    HUNDRED    AM)    KIGHTV    FIGURES   OX   OXE    HUXDREI)   AND   NINE   PLATES,   MANY   OF  WHICH 

ARE    BEAUTIFULLY    COLORED.       THE    DRAWINGS    BY    HERMANN    EABER,    FROM    DISSECTIONS    BY    THE   AUTHOR. 

ALSO,    UPWARDS   OF    TWO    HUNDRED    AXD    FIFTY    WOODCUTS    IN    THE   TEXT. 


SECTION    I.— H  ISTO LOGY. 


E.     O.     SHAKESPEARE,    M.D., 

OPIITIIALMOJ/KHST   TO  THK   PHILADELPHIA    HOSPITAL. 


PHILADELPHIA: 

HENRY   C.    LEA'S   SON   &   CO. 

1882. 


DUNGLISON,  ROBLEY,  M.  D. 

MEDICAL  LEXICON;  A  DICTIONARY  OF  MEDICAL  SCIENCE.  Containing  a  concise  explanation 
of  the  various  subjects  and  terms  of  Anatomy,  Physiology,  Pathology,  Hygiene,  Therapeutics,  Pharmacology, 
Pharmacy,  Surgery,  Obstetrics,  Medical  Jurisprudence  and  Dentistry;  Notices  of  Climate  and  of  Mineral 
Waters;  Formula;  for  Officinal,  Empirical  and  Dietetic  Preparations;  with  the  accentuation  and  etymology 
of  the  terms,  and  the  French  and  other  synonymes,  so  as  to  constitute  a  French  as  well  as  an  English 
Medical  Lexicon.  A  new  edition.  Thoroughly  revised  and  very  greatly  modified  and  augmented.  By 
RICHARD  J.  DUNGLISON,  M.  D.  In  one  very  large  and  handsome  royal  octavo  volume  of  1139  pages.  Cloth, 
$6.50;  leather,  raised  bands,  $7.50;  very  handsome  half  Russia,  raised  bands,  $8. 

STILLE,  ALFRED,   M.  D.,  LL.  D.,  and  MAISCH,  JOHN  M.,  Phar.  D. 

THE  NATIONAL  DISPENSATORY,  CONTAINING  THE  NATURAL  HISTORY,  CHEMISTRY,  PHAR- 
MACY, ACTIONS  AND  USES  OF  MEDICINES,  including  those  recognized  in  the  Pharmacopoeias  of 
the  United  States,  Great  Britain  and  Germany,  with  numerous  references  to  the  French  Codex.  Second 
edition,  thoroughly  revised,  with  numerous  additions.  In  one  very  handsome  octavo  volume  of  1692  pages, 
with  239  illustrations."  Extra  cloth,  $6.75;  leather,  raised  bands,  $7.50;  very  handsome  half  Russia,  raised 
bands  and  open  back,  $8.25. 

FLINT,  AUSTIN,   M.  D. 

A  TREATISE    ON    THE    PRINCIPLES    AND    PRACTICE    OF    MEDICINE.      Designed    for  the  use  of 

Students  and  Practitioners.  Fifth  edition,  thoroughly  revised  and  much  improved.  In  one  large  and  closely- 
printed  octavo  volume  of  1153  pages.  Cloth,  $5.50;  leather,  $6.50;  very  handsome  half  Russia,  raised  bands,  $7. 

THOMAS,  T.  GAILLARD,  M.  D. 

A  PRACTICAL  TREATISE  ON  THE  DISEASES  OF  WOMEN.  Fifth  edition,  thoroughly  revised  and 
rewritten.  In  one  large  and  handsome  octavo  volume  of  Sio  pages,  with  266  illustrations.  Cloth,  $5 ;  leather, 
$6;  very  handsome  half  Russia,  raised  bands,  $6.50. 

PLAYFAIR,  W.  S.,  M.  D.,  F.  R.  C.  P. 

A  TREATISE  ON  THE  SCIENCE  AND  PRACTICE  OF  MIDWIFERY.  Third  American  edition, 
specially  revised  by  the  Author.  Edited  with  additions  by  ROBERT  P.  HARRIS,^!.  D.  In  one  handsome  octavo 
volume  of  655  pages,  with  183  illustrations.  Cloth,  $4;  leather,  $5 ;  half  Russia,  raised  bands,  $5.50. 

SMITH,  J.  LEWIS,  M.  D. 

A  COMPLETE  PRACTICAL  TREATISE  ON  THE  DISEASES  OF  CHILDREN.  Fifth  edition,  thor- 
oughly revised  and  rewritten.  In  one  handsome  octavo  volume  of  836  pages,  with  illustrations.  Cloth,  $4.50; 
leather,  $5.50;  very  handsome  half  Russia,  raised  bands,  $6. 

CORNIL,  V.,  and  RANVIER,  L. 

A  MANUAL  OF  PATHOLOGICAL  HISTOLOGY.  Translated  with  Notes  and  Additions,  by  E.  O. 
SHAKESPEARE,  M.  D.,  Pathologist  and  Ophthalmic  Surgeon  to  the  Philadelphia  Hospital,  and  J.  HENRY  C. 
SIMES,  M.  D.,  Demonstrator  of  Pathological  Histology  in  the  University  of  Pennsylvania.  In  one  very  hand- 
some octavo  volume  of  800  pages,  with  360  illustrations.  Cloth,  $5.50;  leather,  $6.50;  very  handsome  half 

Russia,   raised  bands,  s;. 

DALTON,  JOHN  C.,  M.D. 

A  TREATISE  ON  HUMAN  PHYSIOLOGY.  Designed  for  the  use  of  Students  and  Practitioners  of  Medi- 
cine. Seventh  edition,  thoroughly  revised  and  rewritten.  In  one  very  beautiful  octavo  volume  of  722  pages, 
with  252  elaborate  illustrations.  Cloth,  $5;  leather,  $6;  very  handsome  half  Russia,  raised  bands,  $6.50. 

GRAY,   HENRY,  F.  R.  S. 

ANATOMY,  DESCRIPTIVE  AND  SURGICAL.  The  Drawings  by  H.  V.  CARTER,  M.  D.,  and  Dr.  WEST- 
MACOTT.  The  Dissections  jointly  by  the  ATTIIOR  and  Dr.  CARTER.  With  an  Introduction  on  General 
Anatomy  and  Development  by  T.  HOLMES,  M.  A.,  Surgeon  to  St.  George's  Hospital.  A  new  American  from 
the  eighth  enlarged  and  improved  London  edition.  To  which  is  added  LANDMARKS,  MEDICAL  AND  SURGICAL. 
By  LUTHER  HOLDEN,  F.  R.  C.  S.  In  one  magnificent  imperial  octavo  volume  of  993  pages,  with  523  large 
and  elaborate  engravings  on  wood.  Cloth,  $6;  leather,  $7;  half  Russia,  raised  bands,  $7.50. 


ALLEN'S 


HUMAN  ANATOMY 


HISTOLOGY. 


Entered  according  to  the  Act  of  Congress,  in  the  year  1882,  by 

HENRY    C.    LEA'S    SON    &    CO., 
in  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved. 


CONTENTS. 


HUMAN  ANATOMY. 


INTRODUCTION  . 

DEFINITIONS 

ANATOMICAL  NOMENCLATURE 


HISTOLOGY. 

LYMPH      ....... 

CHYLE 

BLOOD       

ENDOTHELIUM ' 

CONNECTIVE-TISSUE  CELLS 
EPITHELIUM      .... 

The  Epithelium  of  the  Skin 

The  Epithelium  of  Mucous  Membranes 

Glandular  Epithelium 
THE  CONNECTIVE-TISSUE  SYSTEM     . 

Mucous-  or  Gelatinous-Tissue 

White  Fibrous-Tissue 

Yellow  Elastic-Tissue 

Adipose  Tissue 


PAGE 
17 
19 
20 


23 

28 
29 
34 
35 
37 
37 
38 
40 
45 
45 
46 
49 
50 


CARTILAGE 

Hyaline  Cartilage 

Yellow  Elastic  or  Eeticular  Cartilage 

White  Fibrous  Cartilage 
BONE  OR  OSSEOUS  TISSUE 

Ossification  .... 

DEVELOPMENT  OF  BONE    . 

Endochondral  Bone 

Intermembranous  Bone 
TEETH       ...... 

Structure  of  the  Teeth 
MUSCLE 

Smooth  or  Unstriped  Muscle 

Striated  Muscle  .... 

Development  of  Muscle 
BLOODVESSELS  .... 

NERVOUS  TISSUE       .... 

Cerebro-Spinal  Nerves 

Peripheral  Terminations  of  Nerves 

Nerve-Centres     . 

Spinal  Nerve  Ganglia 

Sympathetic  Nerve  Ganglia 
THE  LYMPHATIC  SYSTEM  . 

Lymphatic  Glands       . 


PAGE 

51 

52 

54 

54 

54 

57 

58 

59 

60 

60 

61 

63 

G3 

64 

69 

69 

75 

75 

79 

84 

88 

89 

90 

94 


(iii) 


HUMAN  ANATOMY, 


INCLUDING  ITS 


MEDICAL  AND  SURGICAL  RELATIONS. 


INTRODUCTION. 


IT  is  the  design  of  this  book  to  present  the  facts  of 
human  anatomy  in  the  manner  best  suited  to  the 
requirements  of  the  student  and  the  practitioner  of 
medicine.  The  author  believes  that  such  a  book  is 
needed,  inasmuch  as  no  treatise,  as  far  as  he  knows, 
contains,  in  addition  to  the  text  descriptive  of  the 
subject,  a  systematic  presentation  of  such  anatomical 
facts  as  can  be  applied  to  practice. 

Works  on  anatomy  may  be  placed  in  two  groups : 
those  written  by  scientists  which  have  no  special  ap- 
plication of  any  kind,  and  those  written  by  surgeons 
which  have  a  decided  leaning  to  surgical  application. 
The  model  for  the  latter  group  originated  in  Europe, 
where  the  line  is  sharply  drawn  between  surgical  and 
medical  practice.  It  requires  but  little  discernment 
to  detect  the  faulty  plan  upon  which  both  these  va- 
rieties of  books  are  constructed.  The  scientist  neces- 
sarily lacks  clinical  knowledge  and  sympathy ;  the 
surgeon  lacks  interest  in  all  but  one  class  of  subjects. 
A  book  which  will  be  at  once  accurate  in  statement 
and  concise  in  terms;  which  will  be  an  acceptable  ex- 
pression of  the  present  state  of  the  science  of  anat- 
omy; which  will  exclude  nothing  that  can  be  made 
applicable  to  the  medical  art,  and  which  will  thus 
embrace  all  of  surgical  importance,  while  omitting 
nothing  of  value  to  clinical  medicine — would  appear 
to  have  an  excuse  for  existence  in  a  country  where 
most  surgeons  are  general  practitioners,  and  where 
there  are  few  general  practitioners  who  have  no  in- 
terest in  surgery. 

The  author  may  be  allowed  to  say  that,  in  the 
performance  of  his  self-imposed  task,  nothing  lias  been 


hastily  or  inconsiderately  undertaken.  He  has  been 
actuated  throughout  by  a  sincere  desire  to  produce 
a  useful  book.  He  has  subordinated  all  other  ten- 
dencies and  notions  to  this  end.  In  occasionally 
attempting  a  method  of  treatment  of  a  subject  some- 
what different  from  the  one  usually  accepted,  he 
has  not  departed  from  established  ways  of  teaching 
for  the  sake  of  appearing  to  be  original,  but  for 
good  reasons,  as  he  trusts  will  appear  when  the 
reader  compares  the  text  with  that  of  other  books  on 
anatomy.  The  plan  adopted  is  one  necessarily 
encyclopedic.  The  author  lias  gleaned  his  materials 
from  every  source  accessible  to  him,  and,  so  far  from 
fearing  a  charge  of  plagiarism,  he  will  be  glad  to  have 
the  instances  noted  in  which  he  has  had  the  good  taste 
to  appropriate  an  occasional  apt  phrase  or  striking 
adjective.  There  is  doubtless  a  greater  degree  of 
indebtedness  due  English  works  than  the  author  is 
aware  of,  since  the  powerful  impressions  they  have 
made  on  his  mind  must  remain  unconsciously  to  in- 
fluence his  style. 

By  way  of  introduction  to  the  essential  features  of 
the  volume,  the  attention  of  the  reader  is  invited 
to  the  kinds  of  knowledge  of  the  human  body  the 
physician  demands. 

In  the  first  place,  the  physician  demands  an  exact 
acquaintance  with  the  form  and  construction  of  the 
organs  of  the  body.  But,  inasmuch  as  an  anatomical 
fact  is  of  little  use  unless  the  range  of  the  application 
of  the  fact  is  known,  the  due  connection  between  the 
normal  condition  of  an  organ  and  the  variation  in  the 
condition  of  that  organ  within  the  limits  of  health  will 

(  17  ) 


18 


INTRODUCTION. 


receive  proper  attention.  Accordingly,  the  typical 
description  of  each  organ  will  be  followed  by  a  brief 
statement  of  "  variations." 

In  the  second  place,  the  physician  demands  a 
knowledge  of  the  relations  of  the  parts.  This 
information  it  is  necessary  to  possess  in  performing 
operations  and  in  explaining  signs  or  symptoms. 
Anatomical  relations  may  be  interpreted  to  be  the 
mutual  disposition  of  those  parts  which  occupy  the 
same  neighborhood.  The  local  value  of  relation  has 
been  enforced  by  the  surgeon  whose  accurate  know- 
ledge of  each  special  region  is  held  by  him  to  be  of 
great  importance;  but  the  general  practitioner  cannot 
appreciate  the  necessity  of  keeping  up  ever  refresh- 
ened impressions  of  these  regions.  The  anatomical 
relations  he  needs  are  determined  at  the  examination 
of  the  sick,  or  at  the  autopsy.  While  parts  in  a  given 
region  may  hold  both  surgical  and  medical  rela- 
tions, this  need  not  of  necessi'ty  be  the  case.  In  many 
instances  the  medical  relations  involve  parts  remote 
from  one  another  and  separated  by  one  or  more 
topographical  regions.  The  former  will  receive  the 
name  of  the  topographical  or  the  direct  relation ;  and 
the  latter  the  clinical  or  the  indirect  relation. 

In  the  third  place,  the  physician  needs  some  account 
of  the  uses  of  the  organs.  This  subject  overlaps 
physiological  anatomy.  That  much  only  will  be 
succinctly  given  as  may  be  said  properly  to  illustrate 
the  subject  from  an  anatomical  point  of  view,  and  at 
the  same  time  to  be  free  from  controversy. 

In  the  fourth  place,  the  physician  must  have  a  true 
conception  of  the  nature  and  general  behavior  of 
morbid  processes,  and  of  the  manner  in  which  such 
processes  are  modified  by  locality.  His  comprehension 
of  the  changes  due  to  diseased  action  in  a  given  place 
must  be  fairly  proportional  to  his  knowledge  of  the 
normal  anatomy  of  that  place.  This  subject,  which 
will  receive  the  name  of  localization  of  diseased  action, 
will  be  illustrated  for  the  most  part  by  concise  state- 


ments of  recorded  cases,  in  which  the  essential  feature 
of  each  case  will  be  emphasized  and  the  bearing  it 
has  on  the  subject  treated  of  clearly  shown.  The 
material  in  these  sections  is  capable  of  being  used  by 
the  student  in  two  ways :  first,  in  bringing  forcibly 
to  his  mind  the  value  of  the  facts  themselves,  since 
cases  similar  to  those  quoted  may  occur  to  himself 
after  graduation ;  and,  secondly,  in  lightening  the 
task  of  remembering  important  though  otherwise  un- 
inviting details.  In  a  word,  anatomy  may  thus  be 
made — what  unfortunately  it  rarely  is — an  interesting 
study. 

In  presenting  anatomical  features  in  explanation 
of  given  lesions,  or  of  signs,  or  symptoms,  care  has 
been  taken  to  give  the  sources  of  the  statements  made. 
It  is  hoped  that  the  original  papers  or  volumes  con- 
taining such  statements  will  be  consulted  whenever 
this  is  practicable. 

May  not  a  yet  more  important  use  be  made  of 
these  cases?  May  not  a  series  of  such  abridgments 
be  available  in  assisting  the  practitioner  in  detect- 
ing the  significance  of  obscure  conditions  in  relation 
to  which  the  underlying  facts  are  anatomical  ?  Should 
these  questions  be  answered  affirmatively,  this  book, 
it  is  hoped,  will  take  a  place  among  the  physician's 
volumes  of  daily  reference.  In  order  to  assist  in  the 
attainment  of  this  object  a  copious  index  of  diseases 
and  injuries,  in  addition  to  the  index  of  subjects,  will 
be  appended. 

Among  other  matters,  the  book  will  be  found  to 
contain  an  elaborate  description  of  the  tissues ;  an  ac- 
count of  the  normal  development  of  the  body ;  a  section 
on  the  nature  and  varieties  of  monstrosities;  a  section 
on  the  method  of  conducting  post-mortem  examina- 
tions; and  a  section  on  the  study  of  the  superficies  of 
the  body  taken  as  a  guide  to  the  position  of  the  deeper 
structures.  These  will  appear  in  their  appropriate 
places,  duly  subordinated  to  the  design  of  presenting 
a  text  essentially  anatomical. 


DEFINITIONS. 


19 


DEFINITIONS. 


ANATOMY  is  the  science  that  treats  of  the  enume- 
ration of  organized  bodies,  and  the  description  of 
their  structure. 

HUMAN  ANATOMY  treats  of  the  anatomy  of  man. 

COMPARATIVE  ANATOMY,  as  usually  understood, 
treats  of  the  anatomy  of  all  animals  excepting  man. 
In  a  better  sense,  Comparative  Anatomy  includes  the 
form  and  structure  of  animals  as  related  among  them- 
selves rather  than  as  related  to  man.  The  term  may 
be  also  used  in  speaking  of  the  anatomy  of  the  differ- 
ent races  of  mankind  as  compared  with  one  another. 

DESCRIPTIVE  OR  SYSTEMIC  ANATOMY  treats  of  the 
body  as  classified  by  its  tissues  or  organs.  Thus,  the 
bones,  the  muscles,  the  bloodvessels,  the  viscera,  etc., 
are  severally  distinct  from  one  another.  Descriptive 
Anatomy  is  opposed  to  Topographical  or  Eegional 
Anatomy.  In  this  subdivision  the  body  is  divided 
by  the  relations  of  its  parts  to  one  another  into  a 
.number  of  more  or  less  arbitrarily  defined  regions. 
Surgical  Anatomy  is  a  term  often  used  to  designate 
that  branch  of  topographical  anatomy  which  treats  of 
regions  of  special  importance  in  the  study  of  surgical 
operations  and  of  the  effects  of  injury.  Medical 
Anatomy  is  of  similar  import  to  the  foregoing,  but 
refers  chiefly  to  the  relations  of  parts  as  specially 
considered  by  the  student  of  clinical  conditions  as 
distinguished  from  surgical. 

GENERAL  ANATOMY  treats  of  the  composition  and 
general  relations  of  the  tissues  and  organs.  Thus, 
by  the  general  anatomy  of  bone  are  understood,  first, 
the  composition  of  the  fibrous  tissue,  the  cartilage, 
and  the  salts  contained  in  the  bone;  secondly,  the 
relations  that  these  hold  one  to  another;  and,  thirdly, 
the  consideration  of  similar  structures  or  ingredients 
in  allied  tissues.  The  study  of  the  ultimate  elements 
of  structure,  as  resolvable  by  the  microscope,  has  led 
authors  of  late  years  to  speak  of  this  branch  of  gene- 
ral anatomy  as  Histology  or  Microscopical  Anatomy. 


In  like  manner,  the  chemical  analysis  of  tissue  is 
treated  of  under  the  head  of  Zoo-chemistry,  or  Phy- 
siological Chemistry. 

General  Anatomy  is  opposed  to  Special  Anatomy,  , 
which  deals  with  the  elucidation  of  a  single  part. 
Comparative  anatomists  apply  this  term  to  the  struc- 
ture of  a  single  animal  when  no  comparison  is  en- 
tered upon.  In  this  sense  human  anatomy  itself  is  a 
Special  Anatomy. 

MORPHOLOGICAL  ANATOMY,  or  Morphology,  is  the 
science  of  organic  form,  and  treats  of  homologies  and 
the  comprehensive  relations  of  parts,  especially  those 
relations  indicating  zoological  affinity.  It  is  often  in- 
exactly spoken  of  as  Philosophical  or  Transcendental 
Anatomy.  It  is  opposed  to  Teleological  Anatomy, 
or  Teleology,  which  treats  of  the  adaptations  of  parts 
or  organs  to  certain  final  specific  uses. 

PHYSIOLOGICAL  ANATOMY  includes  the  considera- 
tion of  the  functions  of  organs,  but  in  a  more  general 
sense  than  teleology.  There  is  no  sharply-defined  line 
separating  physiological  anatomy  from  physiology  or 
physics.  The  physiological  anatomy  of  the  eye  is  at 
once  its  physiology,  which,  in  turn,  can  be  explained 
only  by  reference  to  the  principles  of  physics  as  ap- 
plied to  vision. 

MORBID  ANATOMY  is  the  science  which  treats  of 
the  variations  in  the  normal  anatomy  as  determined 
by  diseased  action.  It  is  conventionally  held  to  in- 
clude congenital  defects,  or  gross  variations  in  struc- 
ture: but  these  subjects  are  best  included  under  the 
head  of  TERATOLOGY. 

PRACTICAL  ANATOMY  is  a  term  much  in  use  to 
embrace  the  special  kinds  of  printed  directions  best 
suited  to  those  engaged  in  dissecting,  together  with 
the  methods  of  making  anatomical  preparations,  etc. 
It  may  also  be  said  to  include  the  study  of  human 
anatomy  by  dissection  in  contradistinction  to  the 


20 


INTKODUGTION. 


study  of  human    anatomy  as   a  branch    of  general 
knowledge. 

FCETAL  ANATOMY,  or  EMBRYOLOGY,  treats  of  the 
origin  and  formation  of  the  organs  in  the  embryo. 
As  it  is  naturally  considered  in  connection  with  the 
physiological  anatomy  of  the  organs  of  generation, 
it  is  often  included  under  the  head  of  Physiology. 


DESCRIPTIVE  ANATOMY. — Its  divisions  are  as  fol- 
lows : — 

The  Bones,  or  Osteology. 
"    Joints,  or  Arthrology. 
"    Muscles,  or  Myology. 
"    Bloodvessels,  or  Angciology. 
"    Viscera,  or  Splanchnology. 
"    Nerves,  or  Neurology. 
"     Special  Senses. 


ANATOMICAL    NOMENCLATURE. 


In  this  book  the  word  distal  (following  Barclay) 
will  be  understood  to  refer  to  a  point  away  from  the 
centre  of  the  body  ;  and  the  word  proximal  to  a  point 
toward  the  centre.  For  example,  the  trochlea  of  the 
humerus  is  at  the  distal  extremity  of  the  bone,  while 
the  head  is  at  the  proximal  extremity.  The  word 
central  also  refers  to  a  portion  of  a  nerve  or  vessel 
which  is  connected  with  the  centre  of  the  system  to 
which  the  part  treated  of  belongs.  The  remaining 
portion,  as  opposed  to  the  central,  is  called  peripheral. 
In  the  case  of  the  bloodvessels  the  central  end  is  often 
spoken  of  as  cardiac. 

When  the  axis  of  the  body  or  a  limb  is  understood, 
the  words  median  and  lateral  are  often  used  in  de- 
scribing parts.  Median  means  near  or  related  to  the 
axis  (median  line).  Lateral  means  near  or  related  to 
the  surface  or  periphery,  as  distinct  from  median. 
"Inner"  and  "outer,"  "internal"  and  "external,"  are 
words  very  generally  employed  in  the  same  sense  as 
median  and  lateral.  They  are  less  exact,  however, 
since  they  are  also  used  to  denote  a  central  in  opposi- 
tion to  a  peripheral  part,  as  in  the  contents  of  a  section. 

Median  and  lateral  are  synonymous  with  visceral 
(splanchnic)  and  parietal,  in  describing  surfaces  of  the 
pleura,  pericardium,  peritoneum,  etc. 

A  longitudinal  section  is  a  section  cut  parallel  to 
the  longitudinal  axis  of  the  body  or  limb.  It  may  be 
made  from  before  backward,  when  it  is  called  the 
sagittal  section  (vertico-longitudinal),  because  it  is 
parallel  to  the  sagittal  suture  of  the  cranium ;  or  it 
may  be  made  from  side  to  side,  when  it  is  called  frontal 
(vertico- transverse),  because  it  is  parallel  to  the  frontal 
suture  of  the  cranium.1  The  frontal  section  is,  of 

1  The  terms  sagittal  and  frontal  are  in  general  use  among  Ger- 
man writers.  That  they  relate  to  the  disposition  of  the  cranial 
sutures  is  an  assumption  of  the  writer.  He  cannot  give  the  au- 
thority for  their  first  employment. 


course,  perpendicular  to  the  sagittal  section.  Some 
writers  restrict  the  term  longitudinal  to  the  sagittal 
section,  in  which  case  the  frontal  becomes  to  it  a  dex- 
tro-sinistral  transverse.  It  is  in  this  sense  that  Charcot 
uses  the  latter  term.  The  frontal  section  of  the  cra- 
nium and  contents  becomes  a  true  transverse  section 
of  the  brain,  owing  to  the  angulation  of  the  brain  with 
the  axis  of  the  trunk.  But  a  frontal  section  of  the 
spinal  cord  is  a  longitudinal  section,  since  it  is  parallel 
to  the  axis  of  the  trunk.  With  the  exercise  of  a  little 
care  in  the  use  of  these  terms,  no  confusion  need  occur. 

A  transverse  section  is  a  section  cut  perpendicular 
to  the  longitudinal  axis.  Thus  a  transverse  section 
of  a  limb  is  perpendicular  to  the  axis  of  the  limb. 

A  vertical  section  can  be  opposed  only  to  a  trans- 
verse as  the  author  defines  the  word,  and  may  include 
both  the  frontal  and  the  sagittal.  The  term  should 
be  restricted  to  sections  made  with  direct  reference 
to  the  study  in  which  the  vertical  position  of  the 
part  is  of  importance. 

The  term  horizontal  is  sometimes  used  to  express  a 
section  made  parallel  to  the  plane  on  which  the  organ 
or  approximate  parts  rest.  Thus,  one  can  speak  of  a 
horizontal  section  of  the  brain  and  of  a  horizontal 
semicircular  canal,  because  these  are  parallel  (or  ap- 
proximately so)  to  the  plane  of  the  base  of  the  skull. 

In  a  transverse  section  of  the  parts  confined  in  that 
portion  of  the  trunk,  neck,  or  head  which  contains 
the  large  vessels  Owen  has  named  the  structures  in 
relation  to  the  position  of  the  central  nervous  system 
and  aorta.  Let  it  be  supposed  that  it  is  desired  to 
describe  the  parts  in  a  transverse  section  of  the  thorax; 
then  the  structures  above  the  body  of  the  vertebra  be- 
come neural,  and  those  below  the  body  become  hemal, 
since  the  former  are  near  the  central  nervous  system 
as  expressed  here  in  the  section,  and  the  latter  are 
near  the  aorta.  In  the  same  way  the  section  of  the 


ANATOMICAL   NOMENCLATURE. 


21 


vertebral  canal  becomes  the  neural  space,  and  the 
cavity  of  the  thorax  the  hemal  space.  Anything 
toward  the  neural  space  becomes  neurad;  and  any- 
thing toward  the  hemal  space  becomes  hemad,  etc. 

Ventral  and  dorsal  are  terms  nearly  equal  in  value 
to  those  just  given.  They  more  commonly  relate  to 
surfaces. 

Huxley  proposes  the  terms  epi-axial  and  hypo-axial 
to  designate  the  relation  of  parts  to  any  given  axis, 
either  of  the  trunk  or  of  the  limbs.  According  to 
this  method,  the  longissimus  dorsi  muscle  is  epi-axial 
to  the  axis  of  the  spine,  while  the  psoas  muscle  is 
hypo-axial  to  it.  The  biceps  cubiti  muscle  is  epi-axial, 
the  triceps  is  hypo-axial,  etc.  In  making  these  dis- 
tinctions the  body  is  assumed  to  be  prone  or  supine. 
The  terms  pre-axial  and  post-axial  may  be  substi- 
tuted for  the  foregoing  in  studying  a  body,  like  that 
of  man,  in  the  erect  position. 

In  the  naming  of  organs,  it  must  be  acknowledged 
that  little  order  exists  in  the  employment  of  terms. 


The  terms  are  often  inappropriate,  cumbersome  in 
form,  and  vague  in  meaning.  They  are  as  likely  as 
not  to  be  applied  in  a  manner  at  variance  with  their 
legitimate  use.  Authors  have  multiplied  terms  to 
such  a  degree  that  there  are  but  few  structures  which 
are  designated  by  a  single  name ;  and  since  no  cus- 
tom has  fixed  the  choice  to  be  made  in  such  sy- 
nonymy, clinical  writers  are  perhaps  excusable  in 
consulting  their  own  convenience.  Whenever  prac- 
ticable, the  terminology  used  by  clinical  writers  will 
be  preferred  throughout  this  treatise.  Femurs  will 
have  "  heads"  and  "  necks,"  and  convolutions  will 
continue  to  "  ascend"  or  "  descend,"  as  long  as  prac- 
tical physicians  employ  these  words  in  recording  their 
cases.  With  a  view  of  preventing  confusion,  the 
more  common  of  the  synonymous  terms  will  be  placed 
in  brackets  after  those  adopted  by  the  author.  The 
significance  of  anatomical  terms  not  in  general  use  is 
fully  exhibited  in  works  readily  accessible  to  the 
student. 


HISTOLOGY. 


LYMPH. 


OF  all  the  tissues  of  the  human  frame,  perhaps  the 
lymph  is  the  most  important;  it  is  certainly  one 
of  the  most  extensive.  Possessing  a  volume  nearly 
one-third  that  of  the  entire  body,  it  surrounds  every 
constituent  of  the  connective  framework,  and  is  in  close 
contact  with  the  elementary  parts  of  all  organs.  It 
is  the  ever-present  medium  of  transportation  from 
the  highways  of  the  blood  to  the  cell-elements  of  the 
body,  of  the  pabulum  necessary  to  their  life  and  func- 
tion ;  it  is  the  common  carrier  of  the  products  both  of 
elaboration  and  of  waste  of  the  great  connective-tissue 
system  ;  and  it  is  the  perennial  stream,  through  whose 
agency  the  depuration  of  the  blood,  during  its  course 
in  the  capillaries,  is  balanced  by  a  complementary 
accession. 

The  morphology  of  the  lymph  is  all  that  concerns 
us  in  this  place.  Viewed  from  this  standpoint,  the 
lymph  is  one  of  the  simplest  tissues  studied  under  the 
microscope ;  and  it  is  for  this  reason  that  we  have 
chosen  to  begin  with  it. 

Under  a  high  magnifying  power,  lymph  is  seen  to 
consist,  when  freshly  examined,  of  numbers  of  form- 
elements,  imbedded  usually  in  a  clear,  colorless,  trans- 
parent, structureless  substance  of  a  fluid  consistence 
(the  lymph-plasma).  These  form-elements  may  readily 
change  their  relative  positions  in  the  surrounding 
medium,  by  means  of  currents  in  the  latter,  or  by 
means  of  an  individual  power  of  locomotion  which 
seems  to  be  inherent  in  some.  In  structure,  shape, 
and  dimensions,  these  forms  differ  much  among  them- 
selves, particularly  in  the  warm-blooded  animals;  and 
their  number  in  a  given  volume  of  the  fluid  medium, 
in  which  they  are  loosely  suspended,  varies  greatly  in 
different  parts  of  the  lymphatic  system,  according  to 


the  many  circumstances  which  influence  the  density 
and  chemical  constitution  of  the  lymph-plasma,  as  well 
as  the  activity  of  the  form-elements  themselves. 

The  great  majority  of  these  elements  do  not  differ 
so  much  in  the  general  plan  of  their  construction,  as 
in  the  proportions  of  their  constituent  parts.  Before 
speaking  particularly  of  this,  however,  it  should  be 
well  understood,  that  in  every  collection  of  lymph 
there  are  present  in  the  plasma  forms  in  widely  vary- 
ing numbers  representing  three  general  classes  of 
elements :  (a)  minute  granules ;  (6)  cells  consisting 
of  one  or  more  nuclei,  and  a  protoplasmic  body ; 
(c)  forms  more  or  less  closely  resembling  red  blood- 
corpuscles. 

a.  Minute  granules. — There  are  always  present  in 
every  0.03937  cubic  inch  of  the  lymph  numbers  of 
particles,  which,  under  a  magnifying  power  of  500  or 
600  diameters,  present  the  form  of  very  minute  gran- 
ules; they  are  somewhat  spherical  (sometimes  angu- 
lar), have  a  gray,  opalescent  appearance,  and  are  in  a 
state  of  constant  agitation — thus  exhibiting  the  so- 
called  Brownian  movement.    It  is  the  presence  of  these 
elementary  particles  in  vast  numbers  which  gives  rise 
to  the  opalescence  of  chyle.     A  more  detailed   de- 
scription of  them  will  be  given  when  the  constitution 
of  chyle  is  discussed.     In  the  lymph  their  number 
varies   greatly  in  different  parts  of  the   lymphatic 
system ;  it  varies  also  from  one  time  to  another  in 
collections  made  at  the  same  point. 

b.  Lymph-corpuscles. — The    characteristic   form-ele- 
ment of  the  lymph  is  the  so-called  lymph-corpuscle, 
variously  termed  leucocyte,  white-corpuscle,  or  wan- 
dering-cell. 

Size. — The  lymph-corpuscles  vary  much  in  dimen- 
sions. In  warm-blooded  animals  their  diameter  ranges, 
in  the  thoracic  duct,  from  -5-^5-^  to  -%-fa-Q  of  an  inch, 
while,  in  the  lymph  of  the  peritoneum,  the  size  of 

(23) 


24 


HISTOLOGY. 


many  cells  may  even  reach  J^Q  of  an  inch.  Their 
mean  diameter  is  generally  less  in  the  efferent  than  in 
the  afferent  vessels  of  the  lymph-glands. 

Number. — Their  number  in  a  given  volume  of  the 
plasma  has  been  found  to  vary  quite  as  widely  as  their 
dimensions.  Owing  to  several  causes,  particularly  the 
viscosity  (adhesiveness)  of  the  corpuscles,  the  enumera- 
tion of  these  elements  has  always  been  accomplished 
with  great  difficulty,  and  consequently  with  much  irre- 
gularity as  to  results.  Notwithstanding  this,  however, 
the  data  obtained  tend  to  establish,  with  considerable 
certainty,  the  following  dicta :  1st.  The  number  of 
lymph-corpuscles  in  any  given  volume  of  the  plasma 
varies  widely  in  different  parts  of  the  lymphatic  system. 
2d.  In  the  efferent  lymph-vessels  of  lymphatic  glands 
and  follicles  they  are  much  more  numerous  than  in  the 
afferent  vessels  of  the  same  glands.  3d.  They  are  usual- 
ly much  less  numerous  in  the  smaller  than  in  the  larger 
lymph- vessels  of  the  same  course.  Indeed,  in  many 
locations,  the  small  radicles  of  the  peripheral  lymph- 
capillaries  are  almost  entirely  free  of  lymph-corpuscles. 
4th.  The  small  lymph-spaces  and  lymph-capillaries 
of  the  tendons  and  aponeuroses  contain  almost  none 
in  health,  while  in  the  loose  connective  tissues  lymph- 
corpuscles  are  much  more  abundantly  present. 

In  the  dog,  lymph  from  the  thoracic  duct,  at  one 
observation,  was  found  to  contain  4800  globules  per 
0.03937  c.  i. ;  at  another  time  the  number  reached  7500 
per  0.03937  c.  i.,  while  the  number  of  white  corpuscles 
in  the  blood  was  25000  per  0.03937  c.  i.  In  the  rabbit, 
the  same  observer  (Ranvier)  found  in  the  thoracic 
duct  11300  per  0.03937  c.  i.,  whilst  in  the  blood  of 
the  aorta  only  7500  were  enumerated. 

Minute  constitution. — Both  nucleus  and  cell-body 
consist  of  a  fine  network  of  colorless  albumenoid  ma- 
terial, which  incloses  in  its  meshes  a  semi-fluid  sub- 
stance, usually  also  colorless.  This  network  is  visible 
only  under  very  favorable  conditions,  generally  after 
the  action  of  certain  reagents,  yet  it  has  been  seen  in 
other  cells  of  the  economy  in  situ  natura  during  the 
life  of  the  animal.  The  nuclear  portion  of  this  network 
has  been  termed  the  intra-nuclear,  while  that  of  the 
surrounding  cell-body  has  been  named  the  intra-cellu- 
lar  network;  the  fibres  of  the  two  intercommunicate 
through  the  limiting  membrane  of  the  nucleus.  The 
opalescent  or  finely-granular  appearance  of  this  and  of 
the  preceding  class  of  white  cells  or  lymph -corpuscles 
is  entirely  due  to  the  optical  effect  of  the  fine  fibres 
forming  the  network.  Seen  in  optical  transverse  sec- 
tion these  minute  fibres  appear  as  fine  grayish  granules, 
and  at  the  nodal  or  crossing  points,  resemble  dots  of 
similar  aspect,  the  minute  intermediate  spaces  seem- 


Fig.  l. 


a.  White  blood-corpuscle,  showing 
an  intra-collular  and  an  intra-nuclear 
reticulum.  b.  Elliptical  colored  blood- 
corpuscle,  showing  similar  reticula. 
High  power.  (Klein.) 


ing  more  brilliant.  It  is  this  finely- mottled  appearance 
which  has  suggested  the  use  of  the  term  "finely  granu- 
lar" universally  employed  in  describing  some  cells,  for 
in  many  heal  thy  living  cells  there  are  really  no  granules! 
to  be  found,  a,  Fig.  1,  represents  very  fairly  the  net- 
works already  referred  to.  The  drawing  also  very 
well  shows  the  difference  in  the  closeness  of  the  two 

reticula.  By  reference  to 
the  figure  it  will  be  readily 
observed  that  the  meshes 
of  the  intra-cellular  net- 
work are  much  wider  than 
those  of  the  intra-nuclear 
reticulum.  It  can  now  be 
readily  understood  that 
the  semblance  of  a  granule 
or  pseudo-nucleus  in  the 
cell-body,  or  of  a  spot  or 
pseudo-nucleolus  within 
the  nucleus,  may  be  produced  by  means  of  a  conden- 
sation or  contraction  of  this  reticulum  at  any  point. 

Varieties. — For  convenience  of  description  lymph- 
corpuscles  may  be  divided  into  three  classes — the  ex- 
treme forms  of  each  class,  however,  gradually  shading 
off'  into  those  'of  the  others — as  follows: — 

1.  In  every  specimen  of  lymph  there   are  to  be 
found  small  colorless  corpuscles,  more  or  less  spheroid 
in  shape,  composed  of  a  single  roundish  nucleus,  sur- 
rounded by  an  exceedingly  small  protoplasmic  body. 
In  their  construction  these  small  cells  do  not  visibly 
differ  from  those  of  the  next  succeeding  class,  except 
in  the  relative  proportion    of  nucleus   to  cell-body. 
They  are  present  in  numbers  varying  according  to 
the  location  from  which  the  lymph  may  be  obtained. 
In  the  thoracic  duct  their  number  is  about  equal  to 
the  elements  of  the  second  class,  while  in  the  efferent 
lymph-vessels  of  lymphatic  follicles  or  glands  they 
are  much  more  numerous,  and  in  the  afferent  vessels 
of  the  same  glands  much  less   numerous  than  the 
larger  lymph-corpuscles.     In  the  lymph-glands  them- 
selves these  small  colorless  corpuscles  preponderate  in 
the  medullary  portion,  while,  on   the  contrary,  the 
larger  cells  far  outnumber  the  smaller  in  the  cortical 
portions.     Because   of  the  very  small  protoplasmic 
body  of  these   cells  they  have  frequently  been  de- 
scribed as  free  nuclei.      Their  diameter  is  often  not 
more  than  -5^-$  of  an  inch. 

2.  A  larger  finely  granular  cell,  with  one  nucleus 
about  the  size  of  that  of  the  preceding  variety,  or 
with  two  or  more  smaller  ones,  and  with  a  surround- 
ing cell-body  of  much  greater  extent,  more  or  less 
spherical  in  outline  when  at  rest,  and  composed  of  a 


LYMPH. 


minute  structure  apparently  identical  with  that  of  the 
preceding  forms,  may  be  considered  to  represent  the 
second  class  of  lymph -corpuscles.  In  the  thoracic 
duct,  and  in  the  afferent  vessels  of  lymph-glands,  their 
diameter  often  reaches  2  *0  a  of  an  inch,  while  in  serous 
cavities  it  not  infrequently  measures  ±20 6  °f  an  inch. 
The  cell  consists  essentially  of  two  parts,  nucleus  and 
cell-body.  The  nucleus,  whether  there  be  one  or 
more  contained  within  the  body  of  the  cell,  is  usually 
spheroid,  vesicular,  and  possesses  a  limiting  membrane 
of  double  contour.  When  single,  the  nucleus  is  about 
TTjVff  °f  an  iQca  in  diameter.  During  life,  the  nucleus 
is,  as  a  rule,  invisible,  being  masked  by  the  natural 
slight  opalescence  of  the  cellular  body  surrounding  it. 

3.  The  intra-cellular  reticulum  of  the  lymph-cor- 
puscle may  contain,  in  its  meshes,  besides  a  colorless 
hyaline  semi-fluid  substance,  real  collections  of  colored 
or  highly  refracting  material — genuine  granules.  The 
cell  is  then  called  a  granular  cell.  The  size  of  these 
granular  cells  may  equal  or  exceed  the  dimensions  of 
the  finely  granular  corpuscle,  but  they  are  present  in 
the  Ivmph  in  much  fewer  numbers  than  the  latter. 
The  granules  are  not  distributed  evenly  throughout 
the  cell,  but  may  be  more  or  less  grouped  in  various 
portions.  Their  predilection  is  for  the  body  of  the 
cell.  This  is  so  strong,  indeed,  that  when  seen  during 
life,  light,  areas  are  often  observed  of  considerable 
size  wherein  scarcely  any  granules  are  visible.  These 
lighter  areas  generally  correspond  to  the  position  of 
the  nuclei  when  the  cells  are  motionless. 

The  lymph-corpuscle  is  destitute  of  an  enveloping 
membrane.  When  living,  its  substance  is  soft  and 
gelatinous,  and  extremely  free  to  assume  any  shape 
which  extraneous  or  inherent  forces  may  direct.  Liv- 
ing lymph-corpuscles,  when  removed  from  the  animal 
which  they  inhabit,  and  observed  under  conditions  of 
heat,  surrounding  fluids,  gases,  etc.,  which  are  as 
nearly  as  possible  natural  to  them,  evince  their  vi- 
tality in  numerous  ways,  and  for  longer  or  shorter 
periods. 

Movements.  —  Many  of  these  are  contractile,  and 
when  watched  sufficiently  long  and  close,  exhibit 
various  phenomena  of  an  individual  motion,  which, 
when  energetic  and  protracted,  may  ultimately  result 
in  cell-multiplication  or  locomotion.  This  contrac- 
tility seems  to  reside  in  the  fibres  which  constitute 
the  reticulum,  the  fluid  and  the  granules  which  may 
be  suspended  in  it  having  only  a  secondary  or  passive 
motion.  It  appears  also  that  the  intra-cellular  reticu- 
lum is  usually  much  more  powerfully  active  in  the 
various  movements  of  the  cell  than  is  the  intra- 
nuclear network.  Even  a  movement  which  accom- 
4 


plishes  the  division  of  the  nucleus,  but  stops  short  of 
complete  cell-division,  may  be  effected  almost  entirely 
through  the  agency  of  the  intra-cellular  network. 
Yet  the  intra-nuclear  network  is  by  no  means  en- 
tirely passive.  It  possesses  and  exercises  a  measure 
of  moving  power,  for  certain  reliable  observers  have 
seen  spots  or  nucleoli  move  within  the  nucleus  when 
the  cell  presented  no  other  movements.  During  the 
contractions  and  expansions  of  the  reticulum  the 
fluid  and  the  suspended  particles  contained  in  the 
meshes  are  set  in  motion,  and  currents  more  or  less 
limited  are  thus  produced.  In  this  way  suspended 
particles,  whether  elaborated  in  the  cell  or  imported 
thither,  may  move  from  place  to  place,  while  the 
invisible  contraction  or  expansion  of  the  reticulum 
may  have  a  location  in  the  cell  quite  different  from 
that  of  the  movement  of  the  visible  particles. 

The  lymph-corpuscles  of  the  second  and  third  class 
are,  par  excellence,  those  cells  of  the  lymph  which 
exhibit  active  movements.  The  small  colorless  cor- 
puscles, having  only  a  very  thin  cell-body  around  the 
nucleus,  and  consequently  a  very  small  amount  of 
intra-cellular  network,  as  a  rule,  show  very  feeble 
movements,  or  none  at  all.  When  the  fresh  lymph 
of  a  batrachian  or  mammalian  animal  is,  immediately 
after  extraction,  placed  in  a  moist  chamber  and  prop- 
erly prepared  for  examination  under  a  high  power  of 
the  microscope,  at  first,  the  colorless  corpuscles  are, 
more  or  less,  perfectly  globular,  and  so  opalescent 
that  the  nucleus  cannot  be  seen.  Presently,  if  the 
temperature  of  the  lymph  be  kept  sufficiently  near 
that  normal  to  the  animal  from  which  it  has  been 
taken,  some  of  the  finely  granular,  as  well  as  many 
of  the  granular  corpuscles  are  seen  to  put  forth  from 
one  or  more  portions  of  their  surface  hyaline  masses, 
which  may  persist  indefinitely,  or  be  at  length  with- 
drawn. These  masses,  at  first  hyaline,  or,  in  the  case 
of  the  granular  corpuscles,  free  from  granules,  soon, 
in  a  greater  or  lesser  part  of  their  area,  present  the 
same  optical  appearance  as  does  the  body  of  the  cell. 
They  may  then  increase  in  size  until  perhaps  half  the 
volume  of  the  cell  has,  so  to  speak,  flowed  into  them. 
After  or  before  this  stage  of  alteration  of  form  has 
been  reached,  one  of  two  things  may  happen.  The 
substance  of  the  projection  or  bud  may  sink  back 
again  into  the  original  body  of  the  cell,  which  may 
then  present  its  primary  form,  to  be  perchance  subse- 
quently altered  again  by  similar  manoeuvres ;  or  the 
remainder  of  the  cell -substance  may  continue  to  pass 
into  the  projection,  until  the  latter  has  completely 
absorbed  the  former.  In  the  latter  case,  it  is  evident 
that  the  location  of  the  cell  has  been  changed.  In 


26 


HISTOLOGY. 


this  manner  the  lymph-cells  may  slowly  move  from 
place  to  place.  After  a  considerable  portion  of  the 
substance  of  the  cell  has  passed  into  a  bud  or  projec- 
tion, the  two  main  masses  may  increase  the  distance 
between  their  centres  by  a  lengthening  out  and  thin- 
ning of  the  pedicle  which  unites  them  (see  Fig.  2). 
Subsequently  the  newly-moulded  mass  may  still  flow 
back  into  the  original  cell,  as  before  suggested,  or  it 
may  draw  the  original  or  mother  mass  into  it,  or  the 
two  masses  may  continue  to  separate  until  the  uniting 
bond  becomes  so  fine  that  it  breaks,  when  the  two 
become  independent  individuals,  each  endowed  with 
the  characteristics  of  the  original  cell.  This  is  one 
of  the  modes  of  multiplication  which  the  student  can 
readily  follow.  Instead  of  one  such  budding  mass, 
two  or  more  may  sprout  from  the  original  cell-body, 
and  experience  the  various  changes  already  men- 
tioned. Figs.  2  and  3  very  fairly  represent  the  out- 


Fig.  2. 


Fig.  3. 


WHITE  CORPUSCLES  (OR 
LYMPH-CELLS)  undergoing 
division,  and  active  move- 
ments. High  power.  (Car- 
penter.) 


A  GRANULAR  CORPUSCLE  OF  NEWT,  showing 
changes  undergone  in  fifteen  minutes.  High 
power.  (Klein.) 


lines  which  the  finely  granular  and  the  coarsely  gran- 
ular corpuscles  present  at  various  stages  of  their 
alterations,  although  they  are  drawn  from  white 
blood-cells.  The  structure  of  the  cells,  however,  is 
not  portrayed  with  equal  truthfulness,  the  granular 
aspect  of  the  granular  corpuscles  being  exaggerated 
while  the  nuclei  of  the  finely  granular  cells  are  much 
too  prominent.  The  changes  in  form  already  men- 
tioned are  essentially  those  of  budding  or  gemmation. 
At  the  same  time  that  they  are  transpiring  the 
original  nucleus,  if  there  be  but  one,  may  suffer 
division  either  by  fission  or  gemmation.  Usually 
each  large  bud  draws  into  it  a  nucleus,  if  the  budding 
is  to  result  in  cell-multiplication. 

The  lymph-corpuscle,  instead  of  putting  out  buds, 
may  present  a  constriction  in  the  cell-bodv,  which 
may  progress  until  both  the  nucleus  and  cell  are  cut 


into  two.  Thus,  two  new  cells  may  be  the  result  of 
division  by  scission. 

The  portion  of  the  cell  cut  off'  from  the  original 
mass  in  the  two  ways  above  indicated  may  vary  muoh 
in  size.  Unless  the  new  mass  contain  a  nucleus  it 
cannot  be  regarded  as  a  complete  cell.  Whether  such 
a  nucleated  mass  be  capable  of  development  into  a 
perfectly  formed  corpuscle  endowed  with  powers  of 
reproduction  and  of  ulterior  usefulness  is  a  question 
which  remains  open.  In  every  specimen  of  lymph 
there  are  such  masses  to  be  found,  varying  greatly  in 
size,  but  never  presenting  large  dimensions. 

The  movements  above  considered,  because  of  their 
resemblance  to  those  of  the  uni-cellular  animals  called 
amoebae,  were  termed  by  Max  Schultze  amoeboid 
movements,  and  the  jelly-like  substance  of  which  the 
cells  are  composed,  on  account  of  its  general  resem- 
blance to  the  material  of  certain  vegetable  cells,  re- 
ceived the  name  of  protoplasm. 

Degrees  of  vitality. — The  various  colorless  elements 
of  the  lymph  appear  to  be  endowed  with  different  de- 
grees of  vitality  and  of  activity.  In  every  collection 
of  fresh  lymph  properly  prepared  for  microscopic  ex- 
amination, there  are  some  colorless  corpuscles  which, 
as  long  as  the  examination  is  continued,  remain  un- 
changed, and,  of  those  which  show  signs  of  life,  some 
present  much  more  sluggish  movements  than  others. 
Of  the  immobile  cells,  those  which  show  a  sharply  de- 
fined nucleus,  or  two  or  more  of  the  same  kind,  or  which 
contain  great  numbers  of  fatty  molecules,  may  be  con- 
sidered moribund  or  perfectly  inert,  and  perhaps  already 
advanced  in  the  process  of  disintegration.  Eanvier  re- 
gards these  as  identical  with  varieties  of  pus- corpuscles 
(see  Fig.  4).  Those  which  still  preserve  their  opales- 


PUS-CORPUSCLES. — 1,  a,  6,  in  water ;  c,  d,  e,  after  the  action  of  acetic  acid. 
2,  division  of  nuclei — a,  6,  division  progressing ;  c,  d,  more  or  less  complete. 
( Virchow.) 

cent  finely  granular  appearance,  and  their  nucleus 
partly  or  not  at  all  visible,  may,  for  periods,  remain 
in  a  dormant  state,  and  be  capable  of  being  awakened 
therefrom  by  the  action  of  a  sufficient  stimulant. 

Chemical  and  physical  influences. — Of  the  agents 
which  variously  affect  the  lymph-corpuscles,  some 
of  the  chief  are  heat,  moisture,  oxygen,  acids,  and 
electricity.  Whilst  a  certain  degree  of  heat  is  essen- 
tial, not  only  for  the  manifestations  of  amoeboid 


LYMPH. 


27 


movements,  but  also,  even  for  the  existence  of  life 
in  the  corpuscles,  yet,  on  the  other  hand,  the  tem- 
perature cannot  pass  above  a  certain  elevation  with- 
out endangering  the  life  of  the  cell.  The  two  ex- 
tremes of  heat  within  which  the  amoeboid  cells  are 
active,  seem  to  be  for  the  warm-blooded  animals  about 
70°  and  106^  F.  The  temperature  of  the  lymph  can 
be  brought  much  lower  than  70°  F.  without  neces- 
sarily destroying  vitality.  Indeed,  these  cells  have 
been  seen  to  show  every  phenomenon  of  life  after 
fivc/dng  and  thawing.  Protracted  lowering  of  the  tem- 
perature below  the  extreme,  however,  is  certain  to 
induce  the  death  of  the  cellule.  The  nearer  the  heat 
approaches  the  highest  extreme  the  more  rapid  become 
the  amoeboid  .movements  until  the  limit  is  reached, 
when  they  suddenly  cease  in  the  destruction  of  the 
life  of  the  element,  the  crisis  being  manifested  by  the 
retraction  of  the  amoeboid  prolongations,  the  resump- 
tion of  the  spherical  form  of  the  corpuscle,  and  the  dis- 
tinct appearance  of  the  nucleus,  and  of  the  granules 
contained  in  the  body  of  the  cell.  The  highest  ex- 
treme of  temperature  cannot  be  surpassed  without 
resulting  in  death. 

Not  only  is  warmth  necessary  for  the  life  and  ac- 
tivitv  of  the  lymph-corpuscles  of  warm-blooded  ani- 
mals, but,  according  to  Ranvier,  oxygen  seems  also  to 
be  essential.  When  the  cells  are  deprived  of  it,  they 
become  sluggish,  asphyxiated,  and  finally  die.  Amoe- 
boid movements  of  the  cells  are  excited  by  it,  and 
sluggish  corpuscles  in  which  the  vital  activities  lie 
dormant  or  in  suspense  are  resuscitated  and  put  into 
vigorous  motion.  As  will  be  seen  below,  the  lymph- 
plasma,  especially  in  the  larger  trunks,  contains  only  a 
minimum  of  oxygen,  a  circumstance  in  harmony  with 
the  known  comparative  inactivity  of  the  lymph-cor- 
puscles in  the  passage-ways  of  the  lymphatic  system. 
When  floating  in  a  medium  nearly  devoid  of  oxygen 
their  activities  being,  as  a  rule,  dormant,  their  form 
is  generally  spherical,  and  their  movements  are 
mostly  only  passive.  When  it  is  remembered  that  it 
is  by  means  of  their  amoeboid  movements  that  they 
apply  themselves  to  surfaces,  creep  along,  and  pass 
through  them,  and  that  it  is  upon  these  movements 
their  stickiness  or  so-called  viscosity,  depends,  it  will  be 
readily  understood  how  important  for  the  economy  is 
the  fact  that  in  the  great  lymphatic  system,  where  the 
fluids  move  so  slowly,  and  where,  consequently,  sticky 
elements  could  readily  crowd  together  and  obstruct 
the  channels,  one  of  the  essential  stimulators  of  the 
amoeboid  movements,  oxygen,  should  be  almost  en- 
tirely wanting. 

A  sufficient  fluidity  of  the  elements  themselves  and 


of  their  surrounding  medium  is  also  necessary  for  the 
lively  movements  of  the  lymph-corpuscles.  An  in- 
creased specific  gravity  of  the  plasma  retards,  while, 
vice  versa,  within  certain  limits,  a  lowered  specific 
gravity  accelerates  the  amoeboid  movements.  By  the 
addition  of  water,  in  sufficient  quantity,  to  the  medium 
in  which  the  lymph-corpuscles  float,  the  cellular 
protoplasm  is  swollen  and  made  more  transparent, 
the  nucleus  becomes  distinct,  finally  the  granules 
which  may  be  contained  within  the  cell  assume  the 
Brownian  movement  and  the  cell  dies.  These  va- 
rious phenomena  of  the  death  of  the  cell  become  more 
marked  and  follow  each  other  in  more  rapid  succes- 
sion if  an  acid  be  added  to  the  water. 

Viability.  —  The  viability  of  lymph-corpuscles  is 
great.  Under  favorable  conditions  of  heat  and  oxy- 
gen and  other  surroundings,  they  readily  live  a  long 
time  without  the  organism.  When  properly  pre- 
served they  have  given  evidence  of  life  hours,  days, 
and  even  weeks  after  extraction  from  the  animal. 

Lymph-corpuscles  exposed  in  the  moist  chamber  to 
the  action  of  vapor  of  iodine  become  fixed  and  killed 
the  instant  the  vapor  reaches  them.  Most  of  the 
cells  assume  a  yellow  tint,  while  the  nucleus  and 
granules  become  distinct.  According  to  Ranvier,  a 
few  cells  are  stained  mahogany-brown,  the  color  cha- 
racteristic of  glycogeuic  matter.  This  author  states 
that,  in  these  cells  the  glycogenic  matter  is  diffused 
throughout  the  whole  of  the  element.  It  may  be  ex- 
truded from  the  cell  in  the  form  of  drops,  and  if  the 
action  of  the  iodine  be  sufficiently  prolonged  these 
drops  may  fuse  together  and  form  a  halo  or  atmo- 
sphere around  the  cell  of  a  brown-mahogany  color. 
The  presence  in  the  lymph-corpuscles  of  this  matter 
explains  why  chemical  analyses  have  revealed  the 
presence  of  sugar  in  the  lymph. 

Absorption. — By  means  of  their  amceboid  movements, 
lymph-corpuscles  possess  the  faculty  of  drawing  into 
themselves  minute  particles  with  which  they  come  in 
contact.  They  have  been  seen  also  to  expel  such  parti- 
cles from  within  their  interior.  Thus  they  may  absorb 
minute  particles  at  one  location,  carry  them  for  awhile 
in  their  meanderings,  and  subsequently  discharge  their 
cargo  at  a  distant  point,  to  be  absorbed  perhaps 
again  by  another  living  cell.  This  circumstance  has 
an  important  bearing  upon  the  positiveness  of  deduc- 
tions, respecting  the  nature  of  inflammation,  which 
have  been  drawn  concerning  the  identity,  in  the  tis- 
sues outside  of  the  bloodvessels,  of  lymphoid  and 
other  cells  containing  in  their  interior  minute  foreign 
particles  which  at  some  point  have  been  injected  into 
the  blood-stream. 


28 


HISTOLOGY. 


Lymph-corpuscles  may  become  loaded  with  ab- 
sorbed innocuous  minute  foreign  particles  without 
having  their  activity  seriously  impaired.  Many 
lymph-corpuscles  are  found  which  inclose  in  their 
interior  various  substances  naturally  met  with  in  the 
course  of  their  circulation,  as  for  example  fat  drops, 
granules  of  blood -pigment,  fragments  of  red  blood- 
globules,  and  sometimes  even  small  red  blood-disks. 
Those  cells  which  contain  small  red  blood-disks  have 
given  rise  to  much  dispute  among  physiologists,  some 
believing  that  the  blood-disks  are  formed  within  the 
cell,  others  claiming  that  the  red  disks  reach  their 
singular  location  in  the  same  manner  that  other  ex- 
traneous particles  become  absorbed.  From  their  sup- 
posed power  of  elaboration  of  certain  products,  which 
may  be  discharged  either  as  waste  material  or  as 
matter  to  be  used  by  other  elements  of  the  economy, 
Eanvier  has  suggested  that  the  lymph-corpuscle  is  a 
urn-cellular  wandering  gland. 

c.  Red  corpuscles. — Another  element  constantly  found 
in  the  lymph  is  the  red  blood-corpuscle.  It  is  usually 
met  with  only  in  small  numbers  when  the  lymph  has 
been  very  carefully  extracted.  Its  source  may  be 
traced  to  diapedesis  from  the  blood-capillaries,  which 
doubtless  is  to  some  extent  a  never-ceasing  means  ot 
supply.  But  it  is  also  possible  that  many  may  be  the 
outcome  of  a  new  formation  somewhere  within  the 
lymphatic  system. 

Plasma. — The  plasma  of  the  lymph,  as  has  already 
been  stated,  is,  when  fresh  and  normal,  a  colorless 
transparent  substance  of.  fluid  consistence.  Accord- 
ing toChevreul,  a  thousand  parts  of  the  lymph  of  a  dog 
yielded,  of  water,  926.4;  of  albumen,  61;  of  fibrin, 
4.2 ;  of  salts,  8.4.  In  estimating  the  gases  in  the 
lymph,  Hammarsten  found  in  3.527  ounces  of  fluid 
1.664  cubic  inches  of  gas,  of  which  .054  c.  i.  were 
nitrogen,  .016  c.  i.  oxygen,  and  1.594  c.  i.  carbonic  acid. 
In  consequence  of  the  fibrin-elements  which  it  con- 
tains, the  plasma  of  the  lymph  soon  coagulates  into  a 
gelatinous  mass  when  collected.  If  set  aside  for  a 
while,  this  mass  separates,  like  the  blood-plasma,  into 
two  portions,  the  serum  and  the  clot,  which  latter,  in 
its  elements,  does  not  differ  microscopically  from  that 
of  the  blood. 

CHYLE. 

The  fluid  collected  by  the  lacteals,  transported 
through  the  mesenteric  lymphatic  vessels  and  emptied 
into  the  thoracic  duct  with  the  lymphatic  fluids  from 
other  locations,  is  lymph  which  contains  elements  al- 
ready described.  In  the  intervals  of  digestion,  it  cou- 


Fig-  5.  tains  many  more  minute 

granules  (a,  Fig.  6)  in  a 
given  volume  of  fluid  than 
the    lymph    usually   car- 
ries, but  during  digestion 
the  number  of  minute  par- 
ticles is  so  enormous  that, 
whenviewed  by  the  naked 
eye,    the   chyle    presents 
an  opalescent  appearance, 
which  is  entirely  due  to 
their  increased  numbers. 
The  most  minute  of  them 
usually  exhibit  the  Brown- 
ian    movement.      These 
granules   do    not   consist 
solely  of  fat,  as  some  have 
contended,  but  they  pos- 
sess a  protoplasmic  body 
which  forms  an  envelope 
or  frame  for  the  load  of  fat 
which  each  of  them  holds. 
Under  a  high  power  of  the 
microscope,    after    treat- 
ment with  the  proper  re- 
agents, each  minute  parti- 
cle is  seen  to  consist  of  a 
small  fat-drop  imbedded 
within  a  mass  of  proto- 
plasm, which  envelops  it 
as   a  thin   shell.     Acetic 
acid   added   to   the   fluid 
dissolves     these    delicate 
protoplasmic      envelopes 
and  sets  free  the  fat-glo- 
bules, many  of  which  then 

run  together  to  form  larger  fat-drops  (ft,  c,  Fig.  6). 

When  a  collection  of  chyle  is  placed  in  a  flask,  and 

Fig.  G. 


MOLECULAR  BASE  AND  CORPUSCLES 
OF  CHYLE. — At  a,  from  a  lacteal  ou  the 
intestine  ;  6,  from  a  mesenteric  gland  ; 
c,  from  the  rcceptaculum  chyli.  From 
Man.  (Carpenter.) 


CONTENTS  OF  CHYLE. — At  a,  primary  molecules  of  chyle;  6,  secondary  mole- 
cules of  chyle ;  c,  fatty  globules ;  d,  chyle-corpuscles ;  «,  pale  cells ;  /,  red 
corpuscles.  (Carpenter.) 


BLOOD. 


29 


after  the  addition  of  ether  is  set  aside  for  a  day  or  two, 
there  is  found  at  the  bottom  of  the  vessel  a  deposit 
which  consists  of  lyrnph-corpuscles  and  minute  gran- 
ules. The  latter  have  retained  their  original  globular 
or  angular  shape,  have  become  more  translucent,  and 
have  been  entirely  deprived  of  their  fat. 


BLOOD. 

Like  the  lymph,  the  blood,  when  naturally  flowing, 
consists  of  a  colorless  transparent  fluid  plasma,  in 
which  freely  float  numerous  and  varied  minute  ani- 
mal forms.  The  proportion  of  the  volume  of  these 
form-elements  to  that  of  the  plasma  is  about  as  fol- 
lows: In  1000  parts  of  blood  there  are — 


Water 

Globules    . 

Proteid  substances     . 

Fatty  matter  and  salts 


790. 
127. 

73. 

10. 


Besides  the  fluids  and  solids  above  enumerated,  the 
blood  is  always  more  or  less  charged  with  gases,  of 
which  carbonic  acid,  oxygen,  and  nitrogen  are  the 
chief.  The  capacity  of  the  blood  for  the  absorption 
of  oxygen  is  peculiarly  great,  being  more  than  eight 
times  that  of  water.  Whilst  the  oxygen  of  the  blood 
is  almost,  if  not  quite,  exclusively  held  in  the  red 
corpuscles,  the  carbonic  acid  is  united  with  the  plasma. 

Number  and  size  of  red  corpusc'es.  —  By  far  the 
most  numerous  and  most  important  form-element  of 
the  blood  of  vertebrate  animals  is  the  red  blood-cor- 
puscle, or  red  blood-disk.  We  learn  from  the  enume- 
ration of  Malassez,  that  in  cartilaginous  fishes  the 
number  of  these  elements  ranges  from  140,000  to 
230,000  per  .03937  cubic  inch  (a  cubic  millimetre);  in 
the  osseous  fishes  the  number  varies  between  700,000 
and  2,000,000  per  cubic  millimetre.  The  same  in- 
vestigator places  the  number  of  these  corpuscles  per 
c.  m.  in  birds  at  1,600,000  to  4,000,000,  while  the  ex- 
treme numbers  per  c.  m.  in  the  rnammiferseare  recorded 
at  3,500,000  and  18,000,000.  We  have  the  authority 
of  the  same  writer  for  the  statement  that  the  mean 
volume  of  the  corpuscles  is  almost  always  in  inverse 
ratio  to  their  numbers.  This  proposition  is  not  abso- 
lute, however,  for  a  small  number  of  the  colored 
corpuscles  may  not  be  entirely  compensated  by  an 
increase  in  the  volume  of  the  corpuscle. 

By  consulting  Fig.  7  and  the  table  subjoined,  the 
enormous  difference  in  size,  as  well  as  in  shape,  of  the 
colored  corpuscles  of  the  blood  of  different  vertebrate 
animals  can  be  readily  appreciated.  It  will  be  noticed 
that  the  long  axis  of  the  red  corpuscle  of  the  proteus 


is  recorded  in  the  table  as  T^  of  an  inch,  a  magni- 
tude sufficiently  large  to  be  appreciated  by  the  naked 
eye  under  favorable  circumstances.  Yet  the  colored 
blood-disk  of  the  Amphiuma  (Congo  eel)  is  quite  one- 
third  larger  still. 

Fig.  7. 


Ofl   O  <°  '0 


All  the  corpuscles  here  shown  are  drawn  to  the  uniform  scale,  at  the  bottom 
of  the  wood-cut,  of  l-4000th  of  an  English  inch,  and  the  measurements  are 
expressed  in  vulgar  fractions  of  that  inch.  T.  D,  signifies  transverse  diameter; 
L.  D.  long  diameter;  a.  D.  short  diameter.  (Gulliver.) 


MAMMALIA. 

T.  D. 

L.  D. 

8.  D. 

1.  Ked  Corpuscle  of  Man,  seen  on  the  flat  surface  and 
also  on  the  edge  ;    thickness 

1-12400         .... 

1-3200 

2. 

of  Elephant         .... 

1-2745 

3. 

of  Mask  Deer      .... 

1-1232.5 

4. 

of  Dromedary,  thickness  1-15337 

1-3254 

1-5921 

AVE8. 

5. 

of  Ostrich            . 

1-1649 

1-3000 

Nucleus  of  Ostrich 

1-3200 

1-9166 

6. 

of  Pigeon 

1-2314 

1-3429 

7. 

of  Humming  Bird 

1-2666 

1-4000 

RHPTILIA. 

8. 

of  Crocodile 

1-1231 

1-22S6 

9. 

of  Python 

1-1440 

1-2400 

10. 

of  Proteus 

1-400 

1-727 

PISCES. 

11. 

of  Perch      

1-2461 

3-3000 

12. 

of  Pike         

1-2000 

1-3555 

13. 

of  Shark      

2-1143 

1-1684 

According  to  the  statements  of  various  observers, 
the  mean  number  of  the  colored  corpuscles  in  the 
blood  of  man  may  be  regarded  as  varying  in  health 
between  four  and  five  millions  per  cubic  millimetre. 
The  counts  of  the  corpuscles  made  upon  the  blood  of 
the  same  individual  appear  to  vary  considerably, 
according  to  the  location  whence  the  blood  is  obtained. 
It  seems,  however,  to  be  pretty  well  established  that 
in  any  portion  of  the  economy  where  there  is  a  con- 
densation of  the  plasma  of  the  blood  by  loss  of  fluid, 


30 


HISTOLOGY. 


cither  from  evaporation,  or  from  excretion,  or  the  like, 
there  is  usually  to  be  found  in  the  blood  of  the  part 
an  increased  number  of  corpuscular  elements.  On 
the  contrary,  under  opposite  conditions,  the  number 
of  red  globules  has  usually  been  found  to  be  below 
the  mean.  In  the  left  heart,  and  in  the  large  arteries 
of  the  limbs,  the  number  of  globules  is  identical,  but 
in  the  arterioles  it  is  increased.  The  venous  blood 
of  the  skin,  where  evaporation  is  rapidly  going  on, 
and  the  venous  blood  of  the  kidneys,  where  excretion 
is  taking  place,  is  much  more  rich  in  red  blood- 
disks  per  c.  m.  than  is  the  blood  of  the  corresponding 
arteries.  In  the  interim  of  digestion,  the  mesenteric 
venous  blood  is  richer  in  red  cells  than  is  the  arterial 
blood,  yet  less  rich  in  this  respect  than  the  blood  of 
the  cutaneous  veins.  During  digestion,  however, 
there  are  fewer  red  corpuscles  per  c.  m.  in  the  mesen- 
teric veins  than  in  the  supplying  arteries.  There  is, 
of  course,  in  the  latter  case  an  accession  of  fluid  in 
the  veins  by  absorption  of  the  intestinal  juices.  The 
emptying  of  the  lymph  into  the  blood-stream  at  the 
mouth  of  the  thoracic  duct,  also  causes  a  lowering  of 
the  number  per  c.  m.  of  the  red  corpuscles  in  the  blood- 
current  on  the  proximal  side  of  that  point.  The 
splenic  vein  is  much  richer  in  red  disks  than  is  the 
artery.  The  subhepatic  veins  have  fewer  red  cells 
per  c.  m.  than  have  either  the  portal  veins  or  the 
ascending  cava.  There  is  in  the  liver  a  probable  de- 
struction of  red  globules. 

Besides  these,  so  to  speak,  local  variations  in  the 
number  of  colored  corpuscles  in  a  given  volume  of 
the  blood,  there  is,  perhaps,  a  physiological  mean  varia- 
tion for  each  individual,  as  well  as  a  difference  in  indi- 
viduals dependent  upon  the  conditions  of  sex.  Accord- 
ing to  some  investigators,  there  would  also  appear 
to  be  slight  fluctuations  in  the  mean  volume  of  the 
colored  cells  without  a  marked  disturbance  of  health, 
ts  well  as  differences  in  the  intensity  of  the  coloring 
matter  of  the  corpuscle.  The  same  authors  claim 
that  certain  abnormal  states  of  the  economy  show 
these  fluctuations  in  a  more  or  less  marked  degree. 
Thus  Hayem  declares  that  in  chronic  ansemia  the  mean 
dimensions  of  the  red  'globules  are  always  lessened. 
100  globules  of  anasmic  blood  may  correspond  in 
volume  to  less  than  80  healthy  globules.  At  the 
same  time,  the  intensity  of  the  coloring  matter  of  the 
corpuscles  may  be  lessened  one-quarter  or  one-half. 

The  fresh  fluid  blood  of  vertebrates,  as  is  well 
known,  presents  to  the  naked  eye,  when  seen  by 
reflected  light,  and  in  considerable  quantity,  a  homo- 
geneous opaque  aspect  and  an  intense  red  color.  It 
is  opaque  to  the  naked  eye  for  the  same  reason  that 


an  emulsion  of  oil  is  opaque.  When  spread  out  in  an 
extremely  thin  layer,  however,  and  examined  under 
a  very  high  magnifying  power  by  transmitted  light, 
the  fluid  or  plasma  of  the  blood  is  seen  to  be  per- 
fectly transparent,  colorless,  and  structureless.  The 
form-elements  which  float  in  it  in  enormous  numbers 
are  of  three  general  classes :  colored  cells,  colorless 
cells,  and  minute  free  granules.  The  colored  cells  or 
corpuscles,  instead  of  being  red,  are,  when  examined 
by  transmitted  light,  of  a  slight  orange-green  tint  if 
seen  single,  and  only  approach  a  reddish  tinge  when 
cell  is  imposed  upon  cell  several  layers  deep. 

Form  of  colored  corpuscles. — The  general  form  of  the 
colored  corpuscle  has  been  found  to  vary  greatly  in 
different  orders  of  animals.  In  nearly  all  mammals 
the  outline  has  been  found  circular,  whilst  in  nearly 
all  of  the  lower  vertebrates  it  has  been  seen  to  be 
more  or  less  elliptical.  There  are  a  few  fishes  (the 
lamprey  eel  and  allied  forms),  however,  in  which 
round  colored  corpuscles  have  been  met  with ;  while, 
on  the  other  hand,  two  species  of  mammalian  animals 
(the  camel  and  the  llama)  possess  red  cells  of  oval  out- 
line. A  more  rigid  dividing  line  between  the  mam- 
malian and  the  lower  vertebrate  animals  with  respect 
to  their  colored  blood-corpuscles  is  afforded  in  the 
presence  or  absence  of  a  nucleus.  In  the  lower  ver- 
tebrates, whether  the  red  cell  be  round  or  elliptical, 
there  is  a  central  nucleus  present.  In  the  adult 
healthy  mammalian  corpuscle,  the  nucleus  is  gener- 
ally admitted  to  be  absent.  Nevertheless,  in  oppo- 
sition to  this  latter  statement,  Bcetcher  and  a  few 
others  have  sought  to  prove  the  existence  of  the  re- 
mains of  a  nucleus  in  the  red  corpuscle  of  mammalians 
also  (man,  among  others). 

Varieties  of  colored  corpuscles. — In  the  healthy  blood 
of  adult  man,  the  red  corpuscles  present  two  general 
varieties  of  form  and  dimension— the  red  blood-disk 
or  corpuscle  proper  and  the  microphyte.  Much  the 
more  numerous  of  these  is  the  red  blood-disk. 

The  red  blood-disk  or  corpuscle. — As  the  word  indi- 
cates, instead  of  being  a  spherical  body,  the  red  blood- 
cell  is  flattened  into  the  form  of  a  thin  disk.  Its 
outline  is  naturally  circular,  and  in  fresh  arterial 
blood  the  central  area  of  the  disk  presents  a  concavity 
on  each  side.  In  other  words,  besides  being  circular, 
the  disk  is  normally  bi-concave.  The  edge  of  the  disk 
instead  of  being  sharp  or  acute  is  rounded.  In  con- 
sequence of  its  peculiar  shape,  this  form  of  the 
colored  corpuscle,  when  seen  in  surface  by  trans- 
mitted light  and  properly  focussed,  should  be  most 
intense  in  color  in  the  peripheral  ring  corresponding 
to  the  thicker  portion.  The  color  appears  still  more 


BLOOD. 


31 


•<R> 


HUMAN  BI.OOD-OI.OBFI,ES. — 
rt,  seen  from  the  surface  ;  &, 
from  tho  side;  c,  united  iu 
rouleaux  ;  d,  rendered  spheri- 
cal by  water ;  e,  decolorized 
by  the  same ;  /,  blood-glo-  • 
bulos  shrunk  by  evaporation. 
(Gray.) 


intense  when  the  disk  is  seen  in  profile.  The  colored 
corpuscle  consists  of  three  principal  parts:  the  stroma, 
the  fluid  contents,  and  the  coloring  matter.  Accord- 
ing to  some  late  investigators,  the  body  of  the  colored 
blood-corpuscle  is  composed  of  a  fine  felt-work  of 
minute  fibrillas  (!>,  Fig.  1)  of  an  albuminoid  material, 
holding  in  its  meshes  a  soft 
semifluid  substance.  The  latter 
holds  more  or  less  closely  united 
with  it  the  coloring  matter  of 
the  corpuscle,  a  substance  which 
has  been  named  hemoglobin. 
The  weight  of  authority  seems 
to  incline  to  the  opinion  that 
the  corpuscle  is  membraneless. 
The  red  disk  is  naturally  elas- 
tic, capable  of  assuming  any 
form  which  a  moderate  pres- 
sure may  require,  and  of  re- 
turning again  to  its  original  shape  when  the  pressure 
is  removed.  Many  experienced  and  accurate  observers 
declare  that  they  have  seen  it  manifest  limited  con- 
tractile power.  But  most  writers  assert  that  it  is 
incapable  of  any  other  than  passive  movements,  re- 
garding it  as  a  more  or  less  inert  body,  the  altered 
remains  of  a  once  complete  cell. 

The  red  disks  of  human  blood,  when  the  latter  is 
freshly  drawn  and  spread  out  upon  a  glass  slide  for 
microscopic  examination,  frequently  show  a  marked 
tendency  to  apply  themselves  one  against  the  other 
by  their  broad  surfaces  to  form  rows  similar  to  rou- 
leaux of  coins — -a  phenomenon  the  cause  of  which  is 
unknown. 

Alterations  of  the  red  corpuscles. — The  colored  cor- 
puscle of  man  may  experience  various  alterations  of 
form  and  composition,  which  are  purely  physical  or 
chemical,  in  contradistinction  to  amoeboid  or  vital 
movements. 

Water  causes  them  to  swell,  to  lose  their  bi-convex 
discoid  shape  and  become  more  or  less  spherical,  and 
to  discharge  their  coloring  matter  into  the  surround- 
ing plasma — -which  latter  is  now  uniformly  stained, 
while  the  corpuscle  is  apparently  structureless,  color- 
less, and  sharply  outlined.  Many  solutions  of  salts 
of  less  density  than  that  of  the  blood  have  much  the 
same  action  upon  the  red  corpuscles. 

On  the  contrary,  when  the  density  of  the  blood- 
plasma  or  of  the  artificial  serum  in  which  the  colored 
corpuscles  are  examined  is  increased  either  by  slow 
evaporation  or  by  other  means,  the  surface  of  the  cor- 
puscles, which  is  notably  smooth,  becomes  wrinkled; 
subsequently,  little  prickles  or  spines  appear  all  over 


the  surface  of  the  elements;  finally,  the  corpuscles  be- 
come more  or  less  globular  in  form  and  diminished 
in  diameter,  retaining  the  while  their  prickly  appear- 
ance. They  are  then  known  as  crenated  corpuscles. 
A  few  of  this  kind  of  cells  are  met  with  in  nearly  every 
specimen  of  blood.  The  addition  of  water  causes 
them  to  swell  and  their  spines  to  disappear,  but  they 
retain  the  spherical  form.  Carbonic  acid  causes  the 
bi-concave  disks  to  swell.  When  acting  upon  the 
crenate  corpuscles,  it  causes  the  spines  to  disappear 
and  the  corpuscles  to  partly  resume  their  former  con- 
cave appearance.  The  action  of  this  gas  is  generally 
not  sufficient  to  effect  a  return  of  the  concave  surface 
upon  both  sides,  but  the  corpuscle  is  made  to  assume 
a  saucer  shape. 

A  strong  electric  current  first  causes  the  red  disks 
to  become  crenate  and  spherical ;  afterwards  the  cor- 
puscles swell  and  lose  their  color. 

Bile  causes  the  red  globules  at  first  to  become  pale; 
after  that  they  suddenly  disappear,  leaving  no  trace. 

Urea  causes  the  red  disks  to  become  globular,  but 
does  not  effect  a  decoloration.  Upon  the  surface  of 
the  corpuscle  there  are  formed  little  drops  of  matter 
apparently  entirely  similar  to  the  body  of  the  cell, 
which  are  united  with  each  other  and  with  the  body 
of  the  corpuscle  by  fine  filaments. 

The  addition  of  tannic  acid  in  sufficient  amount  to 
a  portion  of  blood  causes  the  hemoglobin  to  sepa- 
rate more  or  less  completely  from  the  body  of  the 
corpuscle  and  to  form  globular  projections  upon  the 
surface,  of  the  characteristic  color. 

Eapid  desiccation  of  a  thin  film  of  blood,  spread  out 
on  a  glass  slide,  very  perfectly  preserves  the  form  and 
dimensions  of  colored  corpuscles. 

When  blood  is  raised  to  a  temperature  near  134° 
F.,  the  globules  begin  to  lose  their  discoid  form,  and 
to  assume  a  spherical  shape.  At  the  same  time  little 
buds  make  their  appearance  upon  the  surface  of  the 
corpuscle,  united  to  it  and  to  each  other  by  fine  fila- 
ments. When  the  temperature  reaches  158°  F.  the 
globules  become  decolored  and  broken  up  into  small 
transparent  spheres  of  very  unequal  size. 

Cold  causes  a  dissolution  of  the  hemoglobin,  and 
an  effect  similar  to  that  of  water. 

Blood-crystals. —  When  extra vasated  into  the  tis- 
sues, colored  corpuscles  disintegrate  by  breaking  into 
minute  portions,  the  coloring  matter  of  which  finally 
is  transformed  into  brown  pigment-granules,  known 
as  hematin.  Besides  these  granules  of  pigment,  such 
extravasations  may  contain  crystalline  needles  of  a 
reddish-brown  color — hematoidin-crystals.  But  the 
characteristic  crystals  of  the  blood  are  those  of  hema- 


32 


HISTOLOGY. 


globin,  usually  deposited  from  a  considerable  quan- 
tity of  blood.  The  form  of  the  hemaglobin-crystals 
varies  in  different  animals,  and  is  often  quite  peculiar 
to  certain  species.  These  characteristic  forms  often 


Fig.  9. 


°' 


BLOOD-CRYSTALS.  —  A,  trihedral  crystals  from  blood  of  Guinea-pig.  B,  pen- 
tagonal crystals  from  blood  of  Squirrel.  C,  octahedral  crystals  from  blood  of 
Rat  and  Mouse.  D,  heinatin-crystals  from  Human  blood.  E,  hematoidin-crys- 
tals  from  an  old  apoplectic  clot.  F,  hemin-crystala  from  blood  treated  with 
acetic  acid.  (Gray.) 

yield  valuable  suggestions  as  to  the  kind  of  animal 
from  whence  they  came. 

Crystalline  forms,  artificially  derived  from  hemo- 
globin, and  valuable  in  medico- 
legal  examinations  of  supposed 
blood-stains,  are  those  obtained 
from  dry  blood  by  the  action  of 
glacial  acetic  acid.  They  consist 
of  nut-brown,  rhombic,  crystal- 
line plates,  called  Aemz'w-crystals, 
or  hydrochlorate  of  hematin. 

The  red  blood-disk  of  man 
varies  somewhat  in  dimensions. 
Its  mean  diameter,  as  is  seen  by  reference  to  the  table 
on  a  previous  page,  is  about  -5^5-5-  of  an  inch.  This 
size  may  vary  somewhat  among  different  individuals, 
and  in  the  same  person  at  different  times. 

The  microphyte.  —  In  every  specimen  of  human  blood 
there  are  among  the  red  bi-concave  disks,  already  dc- 


HEMIN  -  CRYSTALS,  by 
Teichmaun,  in  hydrochlo- 
rate of  hematin. 


scribed,  a  small  number  of  colored  globular  corpuscles 
of  much  less  diameter,  and  of  a  darker  tint.  Their 
size  may  be  not  greater  than  -^-^  or  -g-J-^  of  an  inch. 
They  appear  to  possess  the  same  intimate  structure, 
and  to  give  the  same  chemical  reactions  as  do  the  red 
bi-concave  disks.  They  have  been  called  microcytes. 
By  some  histologists  they  are  regarded  as  young,  not 
yet  fully  developed,  red  blood-corpuscles  (hemato- 
blasts  of  Hayem),  since  they  seem  to  be  more  numer- 
ous at  times  when  the  blood  is  undergoing  repair. 
By  others  they  are  thought  to  be  the  old  bi-concave 
disks  undergoing  retrograde  changes.  They  are 
especially  abundant  in  progressive  pernicious  anasmia. 

The  white  or  colorless  corpuscles.  —  Of  the  colorless 
corpuscles  of  human  blood,  cells  similar  to  those  of 
the  three  general  classes  of  colorless  cells  described 
as  present  in  the  lymph  are  found,  and  it  is  not 
necessary  here  to  review  their  characteristics.  Their 
number,  however,  is  usually  far  below  that  of  the 
colored  elements.  It  varies  much  even  in  health, 
and  in  the  same  individual,  from  one  time  to  an- 
other. In  comparing  the  white  corpuscles  with  the 
red,  Welcker  has  the  average  as  1  white  to  335  red, 
Moleschott  1  white  to  357  red,  Klein  has  placed  the 
highest  number  in  health  at  1  white  to  650  red.  We 
have  the  authority  of  Moleschott  for  the  statement 
that  boys  have  1  colorless  to  226  colored  corpuscles, 
old  men  1  to  381,  girls  1  to  389,  young  women  men- 
struating 1  to  247,  the  same  women  when  not  men- 
struating 1  to  405,  pregnant  women  1  to  281.  Ac- 
cording to  Hirt  the  proportion  of  white  corpuscles  to 
the  red  is  low  immediately  after  eating,  while  two  or 
three  hours  later,  the  proportion  is  again  near  the 
normal.  The  same  author  states  that  the  proportion 
in  the  blood  of  the  splenic  vein  is  1-60 ;  in  the  splenic 
artery  1-2260 ;  in  the  hepatic  veins  1-170 ;  in  the 
portal  vein  1-740.  It  would  seem  from  these  figures 
that  there  may  be  at  times  a  physiological  leucocy- 
tosis,  although  this  has  been  denied  by  some  later 
investigators.  Groucher  declares  that  the  proportion 
of  the  white  to  the  red  corpuscles  varies  little  in  the 
course  of  the  day.  In  disease  the  relative  number  of 
the  white  corpuscles  has  even  surpassed  the  propor- 
tion of  1  white  to  3  red  cells. 

Red  granular  corpuscles.  • — •  Besides  the  ordinary 
white  corpuscles,  Semrner  has  observed  in  the  blood 
of  mammals  certain  numbers  of  more  or  less  granu- 
lar, nucleated,  colorless  cells,  of  somewhat  larger  size 
than  those  above  considered,  which  contain  red 
granules  of  considerable  size,  and  has  named  them 
red  granular  corpuscles.  According  to  this  author,  as 
well  as  A.  Schmidt,  they  are  probably  intermediary 


BLOOD. 


33 


forms  between  the  white  cell  and  the  red  corpuscle 
of  the  blood. 

Ovoid  colorless  cells. — Von  Eecklinghausen  has  met 
with  a  few  colorless,  ovoid,  granular,  nucleated  cells 
in  the  blood  of  frogs.  In  these  animals  they  seem 
to  bo  more  numerous  in  certain  seasons  of  the  year, 
being  much  more  frequent  in  the  spring  and  summer. 

Many  accurate  observers  have  seen  similar  color- 
less elements  in  the  blood  of  man.  They  have  been 
met  with  chiefly  in  the  blood  of  patients  suffering 
with  certain  febrile  disorders.  In  the  blood  of  re- 
lapsing fever  subjects  they  are  not  infrequent ;  they 
have  also  sometimes  been  encountered  in  typhoid 
fever.  In  the  two  latter  cases  these  cells  are  often 
loaded  with  fine  fatty  granules.  The  writer  has  met 
with  such  cells,  in  some  abundance,  in  inflammations 
aftbeting  the  bloodvessels,  and  believes  with  Sernmer 
that  they  may  be  regarded  as  normal  to  the  blood  of 
certain,  if  not  all,  mammals.  During  the  same  study 
of  inflammation  of  bloodvessels  we  had  the  opportu- 
nity once  or  twice  to  observe  under  the  microscope 
endothelial  cells,  lining  the  vessels,  become  detached 
and  carried  off  in  the  blood-current.  These  observa- 
tions leave  us  no  doubt  that  at  least  some  of  the  ovoid, 
colorless  cells,  above  mentioned,  are  to  be  assigned  to 
a  similar  origin,  namely,  a  limited  desquamation  of 
the  endothclia  lining  the  vessel  walls. 

Free  ijrannles. — The  plasma  of  the  blood  also  car- 
ries in  suspension  numbers  of  minute  particles  appa- 
rently identical  with  the  free  granules  described  as 
present  in  the  lyrnph ;  their  number  as  well  as  their 
nature  varies  in  much  the  same  manner.  Of  course, 
in  the  blood  some  of  these  minute  particles  arise  from 
a  destruction  by  disintegration  and  fragmentation  of 
the  superannuated  red  blood-disks. 

Regeneration. — In  the  blood,  as  in  the  other  tissues 
of  the  organism,  the  various  stages  of  generation,  de- 
velopment, vigorous  activity,  decay,  and  disintegra- 
tion are  constantly  presented  by  the  different  elements. 
After  hemorrhage,  whether  natural  or  accidental,  it 
would  seem  that  the  investigator  has  offered  to  him 
very  ample  opportunity  of  studying  the  methods  of 
regeneration  by  which  immense  losses  of  the  red 
blood-globules  are  rapidly  repaired.  To  replace  the 
ordinary  periodic  destruction  of  red  blood-disks  which 
women  suffer  at  the  time  of  their  catamenia,  about 
one  hundred  and  seventy-five  million  of  red  corpus- 
cles, it  has  been  calculated,  must  be  produced  every 
minute  during  the  intermenstrual  period.  Yet,  the 
question  of  the  renewed  supply  of  colored  elements 
of  the  blood,  notwithstanding  the  many  exhaustive 
investigations  of  hematologists,  has  not  up  to  the 
5 


present  moment  been  satisfactorily  answered.  It 
seems  to  be  generally  admitted,  however,  that  in  some 
way  the  red  disks  are  elaborated  from  the  colorless 
cells,  either  of  the  blood  or  of  the  lymph,  but  the 
diversity  of  opinion  as  to  the  precise  method  of  for- 
mation during  adult  life,  is  great  among  some  leading 
modern  histologists. 

Movements  of  the  corpuscles. — Heat  and  the  other 
reagents  which  were  mentioned  when  considering  the 
elements  of  the  lymph,  have  identical  effects  upon 
the  colorless  cells  of  the  blood.  Wherever  the  cir- 
culation of  the  blood  is  sluggish,  and  heat  and  oxygen 
are  present  in  sufficient  quantities,  large  numbers  of 
the  white  corpuscles  put  forth  active  movements. 
These  movements  are  much  more  energetic  in  the 
small  venules  than  in  any  other  portion  of  the  circu- 
latory system.  It  is  here  and  in  the  capillary  vessels 
that  the  viscosity  or  stickiness  of  the  colored  ele- 
ments especially  shows  itself,  and  it  is  mainly  here 
also  that  the  amoeboid  corpuscles  stick  to  the  walls 
of  the  vessels  and  ultimately  pass  through  them.  The 
fact  that  they  do  traverse  the  walls  of  these  vessels  is 
not  now  questioned ;  but  writers  are  not  yet  agreed 
as  to  the  manner  in  which  the  act  is  accomplished, 
some  believing  that  it  is  effected  by  the  active  creeping 
of  the  corpuscles  through  minute  pores,  which  ordi- 
narily are  filled  with  a  soft  permeable  subs-tance, 
others  claiming  that  the  extravasation  of  the  cor- 
puscle is  passive,  entirely  effected  by  the  outward 
pressure  of  the  blood  against  the  walls  of  the  vessel ; 
still  other  opinions  have  been  advanced.  It  is  ad- 
mitted, however,  that  the  more  active  the  amoeboid 
movements  from  any  cause,  the  more  rapid  and  ex- 
tensive is  the  emigration.  It  has  long  been  known 
that  the  red  elements  also  escape  through  the  vessel 
walls.  The  diapedesis  of  these  elements,  however,  is 
generally  believed  to  be  in  the  main  passive  ;  perhaps 
it  takes  place  through  passage-ways  already  opened 
by  the  previous  emigration  of  a  white  amoeboid  cell. 
In  these  emigrations  of  the  elements  of  the  blood 
through  the  walls  of  the  vessels,  the  cells  are  often 
fragmented,  and  the  fragments  are  according  to  cir- 
cumstances carried  off  by  the  lymph  current  without 
the  vessel  or  by  the  blood  current  within  it. 

Like  the  lymphatic  fluid,  the,  plasma  of  the  blood 
contains  a  certain  proportion  of  fibrin  which  sooner 
or  later  deposits  itself  when  the  blood  is  left  to  stand. 
The  nature  and  structure  of  the  fibrin  of  the  blood  are 
very  similar  to  those  of  the  fibrin  of  the  lymph.  It 
is  supposed  to  be  the  result  of  the  action  of  a  so-called 
fibrinogenous  upon  a  fibrinoplastic  substance  contained 
in  the  plasma. 


HISTOLOGY. 


Derivation  of  blood  and  lymph.— All  the  foregoing 
elements  in  the  lymph  and  in  the  blood  are  to  be 
regarded  as  derivatives  immediately  or  indirectly  of 
the  connective-tissues  of  the  organism — descendants 
from,  the  middle  or  connective-tissue  layer  of  the 
blastoderm,  or  mesoblast. 

ENDOTHELIUM. 

We  now  pass  to  the  consideration,  in  the  endothelia, 
of  another  variety  of  the  connective-tissue  elements 
which  are  widely  distributed.  They  are  flat  cells, 
which  usually  in  a  single  layer  arc  fouud  lining  the 
surface  of  serous  cavities,  the  inner  surface  of  blood-  and 
lymph-vessels,  and  the  synovial  membranes.  They 
consist  of  a  more  or  less  flat  cell-plate,  of  an  albumi- 
nous somewhat  elastic  substance,  and  one  or  more 
nuclei  possessingadouble-contoured  membrane,  amore 
or  less  oval  outline,  and  an  excentric  location  in  the 
body  of  the  cell.  The  cell-plate  consists  of  an  elastic 
network  of  fibrils  (the  intra-cellular  reticulum)  in- 
closing in  its  meshes  a  semifluid  homogeneous  color- 
less substance.  The  nucleus  also  consists  of  a  similar 
but  denser  network  (the  intra-nuclear),  holding  in  its 
spaces  a  similar  semifluid  substance  (see  c,  Fig.  11). 

Fig.  11. 


'I 


CELLS  SHOWIXO  THE  RETIODI.CM  ix  THE  PROTOPLASM  AXI>  NUCLEUS. — a.  Co- 
lumnar epithelial  cell  provided  with  cilia,  the  latter  being  prolongations  of  the 
iutra-ccllnlar  network.  6.  Nucleus  of  a  glandular  epithelial  cell  from  the 
stomach  of  a  Newt,  showing  the  intra-uuclear  network,  c.  Endothelial  cell  of 
the  mesentery  of  a  Newt,  containing  in  a  hyaline  ground-substance  a  plexus 
of  fine  fibre-bundles  —  intra-cellular  network  —  in  connection  with  the  intra- 
nuclear network,  d.  Connective- tissue  corpuscle  from  mesentery  of  X»'\vt, 
showing  very  clearly  the  intra-cellular  network  of  fibrils  and  the  hyaline 
ground-substance  ;  the  former  extends  into  the  branched  processes,  and  is  also 
connected  with  the  more  delicate  intra-nuclear  reticulnm.  e.  Goblet-cell  from 
the  stomach  of  a  Newt,  showing  the  intra-cellular  network  in  connection  with 
fibrils  of  the  intra-nuclcar  network  ;  the  upper  part  of  the  eel!  is  greatly  swollen 
by  mucus.  (Klein.) 

The  cell  appears  to  be  without  a  membrane.  The 
nucleus  is  much  flattened  when  the  cell-plate  is  thin, 
and  causes  a  prominence  corresponding  with  its  loca- 
tion. Normally  the  cell-plate  is  so  thin  and  transparent 


that  its  outlines  are  indistinguishable,  tire  nucleus  alone 
being  visible.  Neighboring  cells  are  placed  nearly  in 
contact  by  their  edges,  being  separated  only  by  a  very 
small  amount  of  structureless  transparent  viscid  sub- 
stance which  holds  them  together.  This  material 
has  been  called  cement -substance  (intercellular  cement). 
When  these  cells  are  seen  in  profile  they  appear  to 
be  more  or  less  linear  or  spindle-form,  the  thickness 
of  the  spindle  corresponding  to  the  nucleus  of  the  cell. 
After  staining  with  a  weak  solution  of  nitrate  of  sil- 
ver, the  intercellular  cement  is  so  darkened  that  the 
outline  of  the  cell  is  made  very  distinct.  It  is  thus 
found  that  endothelial  cells  have  more  or  less  irregular 
polygonal  outlines  (consult  Fig.  12),  and  that  the 

Fiji.  12. 


silver-treated 


NORMAL  EXDOTHBLIBM  OF  VISCERAL  PKRir.inntrM  or  A  1 
and  highly  magnified.     (('Jiapnuin.) 

extent  of  the  cell-plate  is  extremely  variable.  In  the 
arteries  and  larger  lymph-vessels  the  cells  are  more 
or  less  lozenge  shape,  with  the  border  lines  only 
slightly  wavy.  In  the  veins  and  lymph-capillaries. 
the  cells  are  much  broader  as  a  rule,  and  their  periph- 
ery is  represented  by  extremely  irregular  indented 
lines  (consult  figs.  1,  3,  Plate  XII.).  Upon  the  surface 
of  the  serous  cavities  the  outlines  of  the  elastic  cell- 
plates  present  still  another  picture,  as  will  be  seen  by 
reference  to  fig.  1,  Plate  I.  Besides  variations  in 
the  outlines  of  endothelial  cells,  there  are  other  dif- 
ferences which  are  shown  mainly  upon  serous  surfaces 
In  the  adult  animal  the  greater  part  of  these  surfaces 
is  covered  by  a  single  layer  of  extremely  thin,  nearly 
hyaline,  and  somewhat  broad  cell-plates.  There  are, 
however,  limited  areas  more  or  less  numerous  scat- 
tered here  and  there  upon  which  the  cells  offer  a  very 
different  aspect.  They  are  much  narrower,  their  edges 
are  much  less  irregular,  they  are  much  thicker  when 
seen  in  profile  (approaching  a  cubical  form),  are  quite 
granular,  arid  possess  two  or  more  nuclei.  In  fact, 
they  appear  to  be  in  a  decidedly  active  state,  while,  on 


CONNECTIVE-TISSUE   CELLS. 


35 


the  other  hand,  the  vital  proclivities  of  the  first  men- 
tioned very  thin  hyaline  cell-plates  seem  to  be  entirely 
dormant.  These  granular  cells  are  said  by  Klein,  and 
some  others  to  be  germinating,  and  have  been  called 
by  them  germinating  endothelia  (see  e,  fig.  1,  Plate  I.). 
They  are  generally  arranged  around  the  mouth  of  a 
vertical  canal  connecting  a  lymph-channel  of  the  sub 
jacent  connective-tissue  with  the  serous  cavity.  The 
activity  of  this  germinating  endotheliurn  may  be  such 
that  the  granular  cells  proliferate  and  form  new  cells, 
some  of  which  may  be  set  free  in  the  serous  cavity. 
These  new  cells  are  similar  in  every  respect  to  the 
other  lymph-corpuscles  which  float  in  the  lymph- 
plasma,  and  cannot,  after  separation  from  their  place 
of  generation,  be  distinguished  from  them.  The 
endothelia  covering  some  portions  of  the  abdominal 
cavities  and  the  fenestrated  septa  of  the  mediastinum 
are  thus  a  very  fruitful  source  of  supply  of  the  color- 
less corpuscles  of  the  lymph. 

The  endothelia  are,  as  already  stated,  somewhat 
elastic.  When  the  membrane  which  they  cover  is 
stretched,  they  become  thinner,  and  spread  out  in 
order  to  cover  a  wider  extent  of  surface,  and  their 
border  becomes  straighter.  On  the  contrary,  when 
the  membrane  retracts,  their  broad  diameter  lessens, 
their  borders  become  more  sinuous,  and  the  cell  be 
comes  thicker.  Thus  during  full  inspiration  the  endo- 
thelia covering  the  pleural  surface  of  the  lungs  are 
much  thinner  and  broader  than  at  the  end  of  expira- 
tion. At  the  latter  instant  the  pulmonary  endothelia 
are  quite  cubical  in  shape.  • 

As  has  already  been  indicated,  the  endothelia  not 
only  of  the  serous  cavities,  and  of  the  lymph-vessels, 
but  also  of  the  bloodvessels  as  well,  may  be  regarded 
as  some  of  the  sources  of  the  colorless  elements  to  the 
lymph  and  blood. 

CONNECTIVE-TISSUE  CELLS. 

Still  another  group  of  the  elements  derived  from 
the  rnesoblast  is  formed  by  the  cells  of  the  connective- 
tissue.  They  may  be  considered  under  two  general 
heads — the  wandering  cells  and  the  fixed  cells. 

Wandering  cells. — The  wunderiny  cells  of  the  connec- 
tive-tissue are  not  different  from  the  colorless  cells 
already  described  when  considering  the  lymph.  They 
are  in  reality  lymph-corpuscles,  existing  in  the  radi- 
cles of  the  lymphatic  system,  and  do  not  call  for  any 
particular  description  here.  One  form  may  be  con- 
sidered for  a  moment,  however,  before  dismissing 
them.  There  are  found  in  the  interstices  of  the  loose 
connective-tissues  which  are  especially  vascular,  small 


numbers  of  large  granular  corpuscles  slightly  pig- 
mented  (plasmatic  corpuscles  of  Waldeyer).  They  are 
more  frequent  along  the  walls  of  vessels,  and  do  not 
usually  exhibit  marked  amoeboid  movements. 

Connective-tissue  corjmscles. — The  fixed  cells  of  the 
connective-tissue  vary  much  in  shape  according  to  the 
arrangement  of  the  fibrous  tissue  in  which  they  are 
imbedded. 

The  cellular  elements  of  the  great  connective-tissue 
system  are  met  with  only  within  or  upon  the  sides  of 
the  spaces  which  permeate  that  system,  whether  they 
be  in  the  form  of  fine  channels  or  in  the  nature  of 
lymph-cavities,  and  whether  those  spaces  be  large  or 
small.  The  large  spaces,  as,  for  example,  the  perito- 
neal cavity,  the  pleural  cavity,  the  arachnoid  cavity, 
the  heart  and  bloodvessels,  the  larger  Ivmph-vessels, 
are  lined  throughout  by  a  complete  covering  of endo- 
thelial  cells;  the  minute  spaces  which  exist  between 
the  bundles  of  connective-tissue  fibrils  have  as  a  rule 
only  a  more  or  less  incomplete  lining.  But  whether 
the  space  be  of  one  kind  or  of  the  other,  it  is  lined  by 
cells  of  an  essentially  identical  nature;  only  their 
forms  and  the  arrangement  of  some  of  their  structures, 
vary  according  to  the  circumstances  which  surround 
them.  Although  the  fixed  cells  of  the  connective- 
tissue  are  here  considered  under  a  special  section  dif- 
ferent from  that  in  which  the  endothelia  were  dis- 
cussed, it  is  not  because  these  two  species  of  cells 
differ  in  anything  more  than  form. 

The  so-called  fixed  cell  of  the  connective  tissue 
tends  to  assume  a  form  which  is  a  more  or  less  perfect 
mould  of  the  space  in  which  it  is  found.  It  presents 
two  general  forms,  the  one  plate-like,  the  other  stel- 
late. The  plate-like  forms  more  nearly  resemble  the 
cell-plates  of  the  endothelia  than  do  the  stellate  forms, 
and  will  therefore  be  considered  first  (see  c,  fig.  3, 
PI.  IX.). 

Flat  tendon-cells. — In  white  fibrous  tissue  such  as 
tendon,  etc.,  the  spaces  formed  by  the  apposition  of 
several  bundles  are  linear,  and  are  limited  laterally 
by  the  convex  surfaces  of  the  fibrous  bundles.  The 
surface  of  the  space  thus  formed, is  usually  partially 
lined  only.  On  one  side  is  a  longitudinal  row  of  flat 
elastic  cell- plates,  applied  more  or  less  tightly  to  the 
surface  of  the  fibrous  bundles  forming  that  side.  The 
opposite  side  of  this  minute  lymph-space  is  void  of 
cellular  lining.  The  cells  constituting  this  row  are 
placed  edge  to  edge,  and  at  the  line  of  junction  the 
border  of  the  cell  is  quite  straight,  and  generally 
transverse  to  the  direction  of  the  bundle.  These 
cells  thus  have  two  long  straight  parallel  sides.  The 
lateral  borders  of  the  cell  are  more  or  less  notched, 


HISTOLOGY. 


and  sometimes  processes  of  considerable  length,  and 
more  or  less  branched,  spring  from  them.  A  single 
cell  will  generally  spread  across  two  or  more  bundles. 
When  this  is  the  case,  the  indentation  of  the  space 
caused  by  the  convex  surface  of  two  bundles  corning 
together,  is  filled  out  by  the  substance  of  the  cell- 
plate.  In  consequence  of  this  circumstance,  when  the 
cell- plate  is  detached  from  its  position  and  examined 
at  once,  a  ridge  extends  from  one  parallel  side  of  the 
cell  to  the  other  (see  e,  B,  fig.  2,  Plate  III.).  This  ridge 
appears  like  a  band  running  in  the  body  of  the  cell 
when  the  latter  is  viewed  in  surface.  Sometimes  it 
may  be  developed  into  a  secondary  cell-plate  of  some 
width,  springing  from  the  first,  thus  complicating  the 
form  of  the  cell.  These  cells  are  known  as  the  flat 
tendon-cells  of  Ranvier.  They  may  very  justly  be  re- 
garded as  a  special  form  of  endothelium.  The  cell- 
plate  is  elastic,  and  contains  an  ovoid  nucleus  near  one 
straight  side.  It  consists  of  an  intercellular  network 
which  corresponds  Avith  the  extent  of  the  elastic  plate, 


and  at  the  notched  sides  extends  beyond  the  plate 
into  the  processes;  and  the  nucleus  contains  an  inter- 
nuclear  reticulum.  Seen  edgewise,  these  flat  tendon- 
cells  appear  spindle-form,  and  when  seen  in  optical  or 
real  transverse  section  they  present  a  more  or  less 
branched  or  stellate  aspect. 

Stellate  cells. — In  loose  connective  tissue,  or  areolar 
tissue,  where  the  bundles  of  fibrils  intercross  in  every 
conceivable  direction,  the  most  irregularly  formed 
minute  lymph-spaces  are  found.  These  spaces  are 
more  or  less  stellate,  and  they  often  contain  one  or 
more  fixed  stellate  cells.  These  are  the  connective- 
tissue  corpuscles,  par  excellence.  They  lie  in  the  small 
lymph-cavitv,  loosely  attached  to  one  of  the  sides  of 
the  space.  The  simplest  form  of  this  cell  in  adult 
tissue  is  that  of  a  thin  cell-plate  of  more  or  less  irregu- 
lar outline,  and  containing  an  ovoid  nucleus.  The 
nucleus  has  an  enveloping  membrane  of  double  con- 
tour, and  contains  an  intra-nuclear,  very  dense  net- 
work, the  nucleus  seeming  to  be  implanted  nearer  to 


EXPLANATION  OF  PLATE  I. 


Fig.  1.  Peritoneal  surface  of  the  centrum  tendineum  of  a 
Rabbit,  silver-stained  and  highly  magnified.  (After 
Klein.) 

b,  Smaller  endothelial  plates,  situated  over  the  straight 
lymphatic  vessels  which  lie  between  (a)  the  tendon-bundles; 
e,  true  stomata,  some  widely  open,  some  collapsed, — they 
form  a  means  of  communication  between  the  serous  cavity 
of  the  peritoneum  and  those  straight  lymphatics  last  men- 
tioned, and  are  lined  with  endothelial  cells  of  a  germinating 
character;  the  dotted  line  starting  from  c  represents  the 
outline  of  a  lymph-sinus  below  the  surface,  and  in  communi- 
cation with  the  before-mentioned  straight  lymph-vessels. 

Fig.  2.  Highly  magnified  view  of  the  spine-covered  epi- 
thelial cells  of  the  rete  mticosum,  or  deep  layer  of  the 
cutaneous  epithelium.  The  section  is  parallel  with  the 
surface,  and  includes  some  underlying  connective-tis- 
sue. (After  Ranvier.) 

a,  Bloodvessels  with  surrounding  lymph-spaces ;  /,  'con- 
nective-tissue bundles  cut  transversely;  b,  union  of  the  epi- 
thelium with  the  tissue  of  the  cutis ;  e,  polyhedral  epithelial 
cells  of  the  rete  mucosum,  containing  oval  nuclei  and  minute 
brilliant  nucleoli.  These  cells  are  united  together  by  means 
of  their  spines,  c  ;  an  intercellular  cement  fills  the  interspaces 
formed  by  the  spines. 

Fig.  3.  Various  forms  of  epithelium,  fresh  and  much  mag- 
nified.    (After  Ranvier.) 
a,  Thin,  broad,  epithelial   scale  from   the   inside  of  the 


cheek,  showing  a  very  small  nucleus,  and  finely-granular 
contents, — the  imprint  of  adjoining  cells  is  observable  in 
the  innermost  line ;  b,  smaller  epithelia,  from  the  deeper 
epithelial  layers  of  the  bladder,  and  c,  a  larger  epithelial 
cell  from  a  more  superficial  layer  ;  d,  an  isolated  spinous 
epithelial  cell  from  the  rete  mucosum  of  the  skin  ;  n,  the 
nucleus  of  a  ciliated  columnar  epithelial  cell,  whose  vibratile 
cilia  are  shown  at  g  ;  k,  the  elastic  striated  plate  from  which 
project  the  cilia  of  a  smaller  ciliated  columnar  epithelium; 
p,  q,  the  deep  extremities  of  columnar  cells. 

Fig.  4.  Three  isolated  columnar  epithelia  from  the  intestine. 
h,  The  striated  elastic  plate  which  limits  their  free  ex- 
tremity ;  n,  the  oval,  double-contoured  nucleus  of  the  cell. 

Fig.  5.  A.  Profile  view  of  epithelia  of  the  bronchus  of  a 
Rabbit,  showing,  between  the  regular  ciliated  columnar  epi- 
thelium, d,  the  existence  of  branched  cells,  e,  of  a  different 
nature,  whose  processes  form  a  more  or  less  complete  network 
with  each  other,  as  well  as  a  communication  with  the  branched 
connective-tissue  corpuscles,  a. 

B.  A  surface  view  of  the  same  epithelia,  the  letters  hav- 
ing a  similar  indication. 

C.  Shows  a  longitudinal  section  of   a  minute  bronchus, 
d,  Columnar  epithelia.  of  which,  c  are  the  cilia ;  v  is  the 
muscular  coat,  the  smooth   muscle-fibres    being  cut    trans- 
versely ;  a  is  a  lymph-vessel  of  the  adventitious  coat  of  the 
bronchus.     (After  Klein.) 


PLATE 


Fig.l 


Fig.  2 


£   4 


EPITHELIUM. 


37 


one  surface  of  the  cell  than  to  the  other.  This  intra- 
nuclear network  is  in  connection  with  an  intra-ccllular 
network,  which  is  in  part  imbedded  in  the  elastic  cell- 
plate,  but  it  at  some  points  extends  beyond  the  edge 
of  this  plate  to  form  more  or  less  branched  processes 
(see  d,  Fig.  11),  which  attach  themselves  to  the  adja- 
cent fibrous  bundles,  or  to  the  processes  of  other 
branches  or  of  other  cells.  Instead  of  presenting  this 
simple  form,  secondary  cell-plates  may  spring  from 
the  primary  body  and  send  off  processes,  when  the 
connective-tissue  corpuscle  becomes  a  very  complex 
affair.  Yet  it  essentially  consists  of  a  thin  elastic 
plate  similar  to  that  of  the  flat  tendon-cell  already 
described,  and  can  be  classed  in  the  same  category. 

These  fixed  cells  of  the  connective-tissues  are 
believed  by  some  accomplished  histologists  to  be 
capable  of  limited  vital  movements  during  health. 
It  is  undeniable  that  under  the  influence  of  irrita- 
tion they  can,  and  often  do,  return  to  an  active  state, 
when  they  may  put  forth  all  the  powers  of  the  amoe- 
boid lymph-corpuscle. 

EPITHELIUM. 

With  this  subject  we  come  to  the  study  of  a  class  of 
elements  possessing  an  ancestry  and  functions  totally 
different  from  those  of  the  minute  forms  previously 
considered. 

The  cutaneous  epithelia  are  the  representatives  of 
the  epiblast,  or  the  upper  layer  of  the  blastoderm. 
On  the  other  hand,  the  epithelial  cells  of  the  intestinal 
canal  spring  from  the  lower  layer,  or  the  hypoblast 
of  the  blastoderm  of  the  embryo. 

THE  EPITHELIUM  OF  THE  SKIN. 

Sjiinous  cells. — -The  cellular  elements  covering  the 
skin  afford  several  varieties  of  investing  epithelium. 
In  the  rete  mucosum  the  epithelial  cell  is  soft,  appa- 
rently granular,  membraneless,  and  polyhedral  from 
mutual  pressure.  It  is  constituted  by  a  cell-body,  and 
generally  only  one  spherical  vesicular  nucleus.  The 
cell-body  consists  of  a  network  of  fibrils  holding 
in  its  meshes  a  semifluid,  hyaline  substance.  The 
nucleus  also  is  formed  of  a  network,  and  an  inter- 
fibrillar  substance,  and  is  limited  by  a  double-con- 
toured membrane.  There  are  also  in  the  nucleus  often 
one  or  more  small  granules  (nucleoli),  the  remains  of 
a  hyaline,  albuminoid  material,  from  which  the 
nucleus  was  originally  developed.  The  periphery  of 
these  soft  membraneless  cells  of  the  rete  mucosum  is 
furnished  with  small  prickles  or  spines  (see  c,  fig.  2, 


Plate  L),  which  are  frequently  wanting  on  the  peri- 
phery of  neighboring  cells.  These  spinous  cells  have 
been  called  by  various  names,  such  as  the  dentate-cell, 
the  prickle-cell,  and  the  riff-cell.  Adjacent  cells  are 
effectually  held  together  by  the  union  of  their  spines, 
and  by  a  viscid  cement  substance  (intercellular  cement) 
similar  to  that  above  mentioned  for  the  endotheliurn. 

During  irritation  this  cement  substance  increases 
in  amount  but  lessens  in  viscidity.  The  lines  of 
separation  between  the  cells  then  become  quite  dis- 
tinct. Fig.  2,  Plate  I.,  presents  a  very  truthful  picture 
of  the  relations  which  these  cells  bear  to  each  other. 

The  deepest  of  the  rete-cells,  namely  those  in  con- 
tact with  the  fibrous  tissue  of  the  cutis,  are  more  or 
less  columnar,  or  rather  conical  in  form.  The  large 
ends  abut  against  the  polyhedral  rete-cells  previously 
mentioned,  while  the  small  ends  fit  accurately  into 
indentations  of  the  papillary  layer  of  the  derm.  In 
the  dark-skinned  races,  these  columnar  cells  are  more 
or  less  pigmented. 

Stratum  yranulosum,  and  stratum,  lucidum. — The 
outermost  layer  of  the  rete-cells  is  covered  with  a  thin 
lamina  of  flattened,  intensely  granular  cells,  forming 
a  layer  about  two  cells  deep,  the  granular  layer  of 
Langerhans  (see  Fig.  13).  Immediately  external  to 
the  thin  granular  layer  is  a  second,  which  has  received 
the  name  of  the  stratum  lucidum  of  Schron.  This 
layer  is  of  slight  thickness,  the  cells  are  transparent 
and  hyaline,  and  occasionally  exhibit  nuclei. 

Corneous  layer. — Placed  upon  the  stratum  lucidum 
are  the  most  superficial  cells  of  the  cutaneous  epi- 
thelium. They  are  all  converted  into  dense,  corneous 
plates,  with  no  trace  of  their  reticular  or  nuclear 
structure  remaining.  They  form  a  layer  of  variable 
thickness  in  different  locations — the  stratum  corneum, 
or  corneous  layer. 

The  outermost  cells  of  the  rete  mucosum,  or  rete 
Malpighii,  have  lost  their  regularly  polyhedral  form, 
and  have  become  somewhat  flattened,  so  that  in  a 
vertical  section  of  the  skin  they  are  seen  in  profile, 
and  appear  more  or  less  spindle-shaped.  The  cells 
of  the  granular  layer  are  still  more  flat.  Those  of 
the  stratum  lucidum  have  been  flattened  into  mere 
scales,  which,  seen  in  profile,  look  like  interrupted 
lines.  In  the  cutaneous  epithelium  we  have,  there- 
fore, five  varieties  of  epithelial  cells,  named  from 
below  upwards  as  follows:  the  columnar,  granular, 
spinous,  lucida,  and  corneus.  Among  the  soft,  mem- 
braneless, polyhedral  cells  of  the  rete  mucosum  are, 
according  to  some  late  investigators,  a  few  spindle- 
form,  or  stellate  nucleated  cells,  whose  branching  pro- 
cesses run  in  the  intercellular  cement-substance,  and 


38 


HISTOLOGY. 

~«0§j0<x 

Fig.  13. 


st.  I 


VERTICAL  SECTION  OF  THE  HUMAN  SKIN. — a.  Corneous  layer  of  epithelium.  at.  1.  Stratum  lucidum.  gr.  Stratum  grannlosum.  b.  Kate  nmcosum  and  papillary 
layer  of  cylindrical  cells,  c.  Papilla;  of  skin.  d.  Tactile  corpuscle,  e.  Sebaceous  gland.  /.  Hair-bulb,  g.  Erector  pili  muscle,  h.  Convolution  of  swcut- 
gland.  i.  Paciuian  corpuscle,  j.  Pauuiculus  adiposus  (fat-layer),  k.  Vascular  loop.  Low  power.  Partly  diagrammatic.  (Duhring.) 


often  unite  with  the  processes  from  neighboring  cells 
of  a  similar  nature  (see  e,  fig.  5,  Plate  I.).  They  are 
thought  by  some  to  possess  the  characteristics  of  con- 
nective-tissue corpuscles ;  others  believe  them  to  be 
only  amoeboid  lymph-corpuscles ;  while  still  others 
believe  them  to  be  peripheral  nerve-corpuscles  in  com- 
munication, by  their  deep  processes,  with  fine  filaments 
of  the  superficial  cutaneous  nerves. 

The  covering  of  the  skin,  being  composed  of  nume- 
rous layers  of  cells  superimposed  upon  each  other, 
mainly  of  a  flattened  scaly  form,  is  termed  a  stratified 
squamous  epithelium. 

THE  EPITHELIUM  OF  MUCOUS  MEMBRANES. 

Squamous  epithelium. — In  the  mouth  of  man,  the 
epithelial  covering  of  the  mucous  membrane  is  nearly 
identical  with  that  which  covers  and  protects  the  skin. 
The  stratum  granulosum  and  the  stratum  lucidum, 
however,  are  absent.  Moreover,  because  of  the  con- 
stant moist  condition  of  the  epithelial  layers  upon 
this  mucous  membrane,  the  corneous  layer  of  cells  is 
comparatively  thin,  and  is  composed  of  thin  scales  in 
which  small  nuclei  may  be  seen.  The  deep  layer  of 
columnar  cells  is  but  little  piginented.  Some  later 
histologists  note,  throughout  mucous  membranes  and 


the  small  accessory  glands  attached  thereto,  the  exist- 
ence of  a  single  layer  of  flat  endothelial  cells,  between 

Fig.  14 


EPITHELIAL  CELLS  IN  THE  ORAL  CAVITY  OF  MAN  :  a,  large ;  6,  middle-sized  ; 
c,  the  same  with  two  nuclei.     High  power.     (Gray.) 

the  epithelium  arid  the  connective- tissue  upon  which 
it  rests. 


EPITHELIUM. 


39 


The  cellular  covering  of  the  mucous  membrane  of 
the  oral  cavity  is,  therefore,  to  be  regarded  as  a  strati- 
fied pavement  of  squammis  epithelium.  This  is  the 
character  and  arrangement  of  the  epithelium  of  the 
lower  part  of  the  pharynx,  of  the  oesophagus,  the 
edges  of  the  epiglottis  and  of  the  true  vocal  cords,  of 
the  anus,  of  the  intra-vaginal  portion  of  the  cervix 
uteri,  of  the  vagina  and  vulva,  of  the  glans  penis 
and  prepuce,  and  of  the  anterior  third  of  the  nasal 
cavity. 

The  pulmonary  alveoli  are  lined  by  a  single,  some- 
times interrupted  layer  of  squamous  epithelium,  hav- 
ing a  histogenetic  origin  similar  to  that  of  the  epithe- 
lium of  the  bronchi. 

In  the  olfactory  region  of  the  nasal  cavities,  in  the 
upper  portion  of  the  pharynx,  in  the  larynx,  trachea, 
and  bronchi,  the  cellular  investment  consists  of  a 
stratified  columnar  ciliated  epithelium.  In  the  Fallo- 
pian tubes  and  in  the  fundus  uteri  and  extra-vaginal 
portion  of  the  cervix  uteri,  the  mucous  membrane  is 
covered  by  a  single  layer  of  ciliated  columnar  epithe- 
lium. The  internal  surface  of  the  stomach  and  intes- 
tines is  lined  by  a  sim2>le  columnar  epithelium. 

Simple  columnar  epithelium. — The  columnar  epithelial 
cell,  when  it  presents  one  of  its  ends  upon  a  free  sur- 
face, usually  is  limited  at  that  end  by  a  thin  plate  of 
considerable  stiffness,  which  seen  edge-wise,  as  when 
the  cell  is  viewed  in  profile,  appears  like  a  brilliant 
band.  In  the  simple  columnar  cells  of  the  intestinal 
canal,  under  favorable  conditions,  this  brilliant  band 
scums  to  be  vertically 
striated  (see  Fig.  15). 
By  violence  the  thin 
limiting  plate  is  often 
partially  or  completely 
detached  from  the  end 
of  the  cell.  Frequently 
the  cell  possesses  a  very 
delicate  limiting  mem- 
brane, which,  however, 
is  probably  only  a  con- 
densed film  of  the  body 
of  the  cell.  The  colum- 
nar cell  is  somewhat 
soft  and  pliable,  and 
may,  therefore,  readily 
assume  shapes  imposed 
upon  it  by  pressure.  It 
is  rarely  absolutely  co- 
lumnar; it  is  frequently  more  nearly  conical.  Often 
its  deep  end  divides  into  two  or  more  short  thick 
branches  (see  p,  fig.  3,  Plate  I.).  It  is  provided  with 


Fig.  15. 


SECTION  OF  A  VILLCTS  OF  A  RABBIT,  fur- 
nishing examples  of  non-ciliated  colum- 
nar epithelium.  High  power.  (Strieker.) 


a  nucleus  which  is  oval  or  more  or  less  rod-shaped 
possesses  a  thin  membrane  of  double  contour,  and 
generally  one  or  more  distinct  nucleoli.  The  nucleus 
is  usually  located  near  the  deep  extremity  of  the  cell. 
The  body  of  the  cell  is  composed  of  a  network  of 
fibrils,  whose  meshes  have  a  decided  linear  shape, 
mainly  parallel  with  a  long  axis  of  the  cell.  The 
nucleus  also  contains  a  network  which,  like  the  nuclei 
of  other  cells,  is  denser  than  that  of  the  cell-body. 
The  finely  granular  appearance  of  the  cells  is  due  to 
the  existence  of  this  reticulum.  The  semifluid  mate- 
rial contained  in  the  meshes  of  the  reticulum  may 
vary  in  amount,  and  cause  the  interfibrillar  spaces  to 
increase  more  or  less  in  extent,  thus  increasing  or 
lessening  thereby  the  granular  aspect  of  the  whole  or 
a  part  of  the  cell. 

Ciliated  columnar  epithelium. — The  ciliated  colum- 
nar epithelium  is  essentially  similar  in  structure  to 
the  simple  columnar  cell.  It  differs  from  the  latter 
only  by  the  presence  of  a  number  of  fine  cilia  or  hairs 
vertically  attached  to  the  thin  plate  at  the  free  ex- 
tremity of  the  cell  (see  g,  fig.  3,  Plate  I.).  These 
cilia  pass  through  the  thin  limiting  plate  and  are 
directly  attached  to  the  fibres  of  the  intra-cellular 
reticulum  (see  a,  Fig.  11).  During  the  life  and  the 
activity  of  the  cell  the  cilia  are  in  more  or  less  vigor- 
ous vibratile  motion,  and  those  agents  which  excite 
or  retard  movements  in  the  amoeboid  corpuscles  have 
the  same  action  upon  the  movements  of  the  cilia! 

In  stratified  ciliated  columnar  epithelial  coverings, 
the  ciliated  columnar  cells  constitute  the  superficial 
layer.  They  are  usually  present  in  a  single  row.  Be- 
tween and  below  the  deep  extremities  of  these  ciliated 
cells  are  a  greater  or  lesser  number  of  spindle-form  and 
more  or  less  irregular  polyhedral  epithelial  cells. 
These  are  usually  membraneless,  and  contain  one  or 
more  spherical  nuclei,  the  minute  structure  of  the  cell 
being  reticular.  Scattered  here  and  there  among  the 
columnar  and  other  cells  are  a  few  soft  granular 
membraneless  bodies,  sometimes  fusiform,  sometimes 
branched,  apparently  similar  to  the  analogous  cells 
mentioned  under  the  cutaneous  epithelium  (see  e,  fig. 
5,  Plate  I.). 

Goblet-cells. — Some  of  the  columnar  cells,  whether 
ciliated  or  not,  may  become  distended  and  distorted 
with  a  collection  of  mucus  near  the  free  end.  Such 
cells  are  known  as  goblet-cells  (see  e,  Fig.  11).  The 
nucleus  is  generally  pressed  aside  and  crowded  into 
the  deep  end  of  the  cell.  If  the  accumulation  of  the 
mucus  continue,  the  thin  limiting  plate  is  broken  or 
detached,  an  occurrence  which  results  in  the  dis- 
charge of  mucous  drops  upon  the  free  surface  of  the 


40 


HISTOLOGY. 


epithelium,  and  the  probable  ultimate  destruction  and 
desquamation  of  the  cell.  During  the  progress  of 
gastric  digestion,  these  goblet-shaped  columnar  cells 
are  to  be  found  in  great  numbers  upon  the  mucous 
coat  of  the  stomach. 

The  epithelial  cells  of  the  mucous  membranes,  like 
those  of  the  skin,  are  slightly  separated,  yet  closely 
and  firmly  held  together  by  an  intercellular  cement. 
According  to  the  investigations  of  some  authors 
(Klein  among  others),  foreign  particles  placed  upon 
the  surfaces  of  mucous  membranes  are  absorbed 
mainly,  if  not  exclusively,  by  means  of  the  intercel- 
lular cement-substance,  which,  at  the  surface  of  the 
fibrous  tissue,  is  in  direct  communication  with  the 
superficial  lymph-spaces  of  the  connective -tissue. 
Even  in  the  intestines  the  minute  particles  of  the 
chyle,  according  to  Klein,  are  not  taken  up  by  the 
columnar  cells,  and  thence  passed  into  the  radicles  of 
the  lacteals,  but  they  enter  the  intercellular  cement, 
which  reaches  the  free  surface,  and  pass  along  this 
until  they  reach  the  lacteal  capillaries. 

GLANDULAR  EPITHELIUM. 

Under  this  caption  we  consider  cells  of  widely- 
varying  function  and  location.  As  a  rule,  they  have 
an  embryonal  derivation  similar  to  that  of  the  invest- 
ing epithelium,  upon  which  the  ducts  of  their  glands 
empty.  In  fact,  they  commonly  begin  to  develop  at 
an  early  period  of  intra-uterine  life  by  epithelial 
buds,  which  project  from  the  deepest  layers  of  this 
investing  epithelium  into  the  subepithelial  connective- 
tissue. 

Glands  of  mucous  membranes. — The  epithelial  glands, 
which  open  upon  the  surface  of  mucous  membranes, 
seem  to  be  constructed  upon  two  general  plans,  if  we 
are  to  judge  from  the  nature  of  their  lining  epithelium. 
The  various  forms  of  these  glands  seern  to  be  only 
modifications  of  two  models. 

1.  Simple  tubular  mucous  ijlands. — The  simplest  kind 
of  epithelial  gland  is,  perhaps,  the  crypt  or  follicle 
of  Lieberkuhn.  It  usually  presents  the  form  of  a 
small  tube,  closed  at  the  deep  extremity  by  a  caecal 
end,  and  opening  at  the  other  upon  the  surface  of 
the  intestinal  canal.  The  cells,  lining  the  tube  in  a 
single  layer,,  are  apparently  identical  in  structure 
and  form  to  the  columnar  epithelium  of  the  surface. 
They  are  short,  cubical,  or  columnar  cells,  which 
possess  a  spherical  or  oval  nucleus,  with  a  thin, 
double-contoured  limiting  membrane.  The  gland- 
tube  is  usually  single,  but  sometimes  may  be 
branched  in  its  deep  extremity.  The  deeper  por- 


tion of  the  gland  is  frequently  slightly  larger  in 
diameter  than  is  the  upper  portion  or  neck  of  the 
gland.  In  the  wider  portion  the  cells  are  longer. 
The  columnar  cells  consist  of  a  network,  which  is 
denser  in  the  nucleus  than  in  the  cell-body.  The 
fibres  of  the  reticulum  have  a  general  direction 
parallel  with  the  long  axis  of  the  columnar  cell, 
namely,  perpendicular  to  the  wall  of  the  tube.  They 
are  separated  from  the  latter  by  a  thin,  flat,  sometimes 
branched,  endothelial  cell,  and  separated  from  their 
neighbor-cells  by  a  small  amount  of  cement-substance, 
into  which  sometimes  branches  of  the  endothelial 
cells  above  mentioned  may  project.  The  free  end 
of  the  columnar  cell  may  contain  a  drop  of  mucus, 
when  it  constitutes  what  has  already  been  described 
as  the  goblet-cell.  The  chief,  if  not,  indeed,  the  only 
function  of  these  cells  is  the  secretion  of  mucus,  and 
the  gland  itself  may  be  regarded  as  the  simplest  form 
of  a  mucous  gland.  The  cells  in  the  quiescent  stiite 
are  smaller,  and  apparently  more  granular  than  when 
the  cell  is  actively  forming  and  excreting  mucus. 
At  no  time,  however,  during  health,  is  the  cell 
coarsely  or  densely  granular.  It  is  to  be  remarked 
also  that  the  longitudinal  striation  of  the  cell — an 
appearance  in  itself  due  to  the  prevalent  longitudi- 
nal direction  of  the  meshes  of  the  intra-cellular  and 
intra-nuclear  reticula — is  somewhat  more  marked  in 
the  neck,  and  at  the  orifice  of  the  gland,  than  in  its 
fundus.  Besides  the  foregoing  characteristics,  these 
purely  mucous  tubular  glands  possess  a  distinct 
lumen  throughout  their  length. 

2.  Compound  tubular  mucous  glands. — In  the  mucous 
glands  of  the  mouth  we  have  an  example  of  a  com- 
pound tubular  gland,  whose  chief  function  is  the  ex- 
cretion of  mucus.  Here  we  have  not  only  a  modifi- 
cation of  the  form  of  the  simple  tubular  gland,  but 
there  is  also  a  complication  of  the  lining  of  the  tubes. 
Some  of  the  largest  of  these  glands  may  be  taken  as 
a  type  for  description.  Each  gland  consists  of  a  large 
duct,  funnel-shaped  at  its  mouth.  The  duct  passes  more 
or  less  obliquely  through  the  mucosa.  Reaching  the 
submucous  tissue  it  divides  into  a  number  of  smaller 
tubular  branches,  each  of  which  soon  slightly  enlarges 
to  form  an  infundibulurn.  Very  soon  the  infundi- 
bulum  again  narrows,  and  passes  into  the  secreting 
portion  of  the  tube,  which,  after  turning  irregularly 
in  numerous  convolutions,  ends  in  a  csecal  extremity. 
In  man,  the  funnel-shaped  mouth  of  the  duct  has  a 
lining  of  stratified  pavement  epithelium.  At  a  slight 
depth,  however,  the  epithelial  lining  of  the  duct  is 
seen  to  consist  of  a  single  layer  of  long,  narrow 
columnar  cells,  with  intra-cellular  and  intra-nuclear 


EPITHELIUM. 


41 


networks,  producing  a  distinct  longitudinal  striation, 
and  a  slightly  granular  appearance  of  the  cell.  The 
lumen  of  the  duct  has  considerable  width.  In  the 
narrow  tubes,  into  which  the  duct  branches,  the  epi- 
thelium is  still  in  a  single  layer  only,  but  the  cells 
are  now  much  shorter  and  wider.  They  may  be 
cubical,  or  even  more  flattened.  The  cells  still  con- 
tain networks,  but  these  are  neither  dense  nor  arranged 
so  as  to  produce  an  apparent  striation. 

In  the  infundibulum  the  lining  epithelium  still  pre- 
serves this  more  or  less  flattened  form.  The  lumen  of 
the  infundibulum  is  consequently  comparatively  wide. 
As  the  deep  portion  of  the  infundibulum  is  reached 
it  again  slightly  narrows  to  pass  into  the  convoluted 
tubes.  At  the  same  time  the  character  of  the  lining 
epithelium  again  changes.  Their  cells  now  become 
columnar  and  very  slightly  granular.  They  contain 
a  round  or  oval  double-contoured  nucleus,  which  is 
located  near  the  outer  end  of  the  cell,  both  cell-body 
and  nucleus  consisting  of  a  network  of  fibrils  forming 
comparatively  large  meshes  when  the  gland  is  fully 
developed.  When  the  latter  is  active,  these  cells  con- 
tain drops  of  mucin  in  their  inner  portion,  and  present 
every  characteristic  of  goblet-cells.  When  exhausted, 
they  shorten  very  considerably  and  become  very 
granular,  and  consequently  somewhat  opaque.  The 
lumen  of  the  convoluted  tube  is  characteristically 
large.  The  epithelia  of  these  glands  rest  upon  a  layer 
of  endothclial  or  connective-tissue  cells  which  are 
more  or  less  branched,  some  of  the  branches  penetrat- 
ing as  septa  between  the  intercellular  cement  which 
holds  the  cells  together. 

Sometimes  in  the  convoluted  portion  of  the  glands 
two,  three,  or  more  embryonal  cells  are  found  at  rare 
intervals  along  the  course  of  the  tube  massed  together 
in  thin  clumps,  and  they  are  always  located  between 
the  previously  described  columnar  epithelium  and  the 
layer  of  endothelial  cells  which  form  the  basement- 
membrane  of  the  tubes.. 

The  sublingual  gland  of  man  and  the  submaxillary 
gland  of  the  dog  are  mucous  glands  still  larger  than 
those  last  considered,  but  they  are  constructed  upon 
the  same  general  plan  with,  however,  an  epithelial 
lining  a  little  more  complicated.  In  the  convoluted 
portion  of  the  tubes,  protoplasmic  collections  between 
the  mucus-cells  and  the  basement-membrane  of  stel- 
late endothelia,  somewhat  similar  to  the  embryonal 
cells  mentioned  as  occasionally  present  in  the  last- 
described  mucous  glands  of  the  mouth,  are  in  these 
glands  very  numerous.  These  protoplasmic  masses 
are  more  or  less  crescentic,  and  have  received  the 
name  of  the  crescents  of  Gianuzzi,  after  the  anatomist 
G 


who  first  accurately  described  them.  They  are  densely 
granular  uni-  or  poly-nucleated  masses  without  a  de- 
fined membrane,  but  with  projections  which  fit  into 
the  spaces  between  the  epithelial  cells  with  which 

Fig.  16. 


—a, 


StTBMAXIl,l,ARY  GLAND  op  Don. —a.  Mucns-colls.  b.  Protoplasm  cells,  a. 
Crescents  of  Gianuzzi.  d.  Traunverse  section  of  excretory  duct  with  its  pecu- 
liar columnar  cells.  High  power.  (Strieker.) 

they  are  in  contact.  In  other  respects  the  contents 
of  these  compound  tubular  glands  are  apparently 
identical  with  those  of  the  smaller  mucous  glands  of 
the  mouth. 

3.  Compound  tubular  salivary  glands. — The  parotid 
gland  of  man  is  built  upon  the  same  plan  as  is  the 
sublingual  so  far  as  the  arrangement  of  the  tubes  is 
concerned,  but  its  function  is  quite  different,  and  so 
also  are  the  characters  of  the  lining  epithelia  of  the 
convoluted  secreting  tubes.  The  epithelial  cells  of 
this  portion  of  the  tubes  are  more  or  less  cubical, 
and  are  densely  granular  and  proportionately  opaque. 
They  contain  a  round  nucleus  located  near  the  base- 
ment-membrane, and  limited  by  a  thin  envelope  of 
double  contour.  The  nucleus  arid  cell-body  consist 
of  a  dense  network  of  fibrils  with  irregular  and  small 
meshes,  containing,  in  the  quiescent  state,  a  minimum 
of  fluid  substance.  During  activity,  this  fluid  in- 
creases very  considerably,  and  distends  the  meshes, 
thus  causing  the  cell  to  become  considerably  larger 
arid  more  transparent.  Crescents  of  Gianuzzi  are  found 
in  these  tubes  also,  but  in  fewer  numbers  than  in  the 
purely  mucous  glands.  Another  distinction  between 
these  purely  salivary  glands  and  the  purely  mucous 
glands  is  in  the  diameter  and  the  size  of  the  lumen 
of  the  convoluted  tube.  In  the  mucous  gland  the 
lumen  is  distinctly  recognizable,  of  considerable  size, 
and  is  generally  patulous,  while,  on  the  contrary,  in 
the  purely  salivary  glands  it  is  often  doubtful  if  the 


42 


HISTOLOGY. 


convoluted  tube  has  a  real  lumen.  It  is  at  all  times 
so  small  and  generally  so  plugged  with  a  substance 
much  like  the  intercellular  cement,  that  some  authors 
have  denied  the  existence  of  a  true  lumen  in  this 
portion  of  the  tube,  and  have  claimed  that  the  small 
intercellular  spaces  act  the  part  of  a  duct  for  the 
secretions. 

In  the  submaxillary  gland  of  man  we  have  presented 
a  large  compound  tubular  gland  still  more  compli- 
cated than  either  the  large  purely  salivary,  as  the 
parotid,  or  the  large  purely  mucous,  like  the  sublin- 
gual,  for  in  this  gland  the  functions  and  the  structure 
of  the  two  latter  seem  to  be  united  in  one.  It  is  a 
compound  tubular  gland  of  mixed  function — the 
secretion  of  a  salivary  fluid  and  the  excretion  of 
mucus,  and  it  combines  more  or  less  intimately  and 
perfectly  the  anatomy  of  each.  Some  of  the  lobules 
of  the  gland  are  composed  of  convoluted  tubules, 
which  possess  an  entirely  salivary  character,  while 
others  present  a  purely  mucous  structure  and  func- 
tion. Further,  even  in  the  same  lobule,  some  of  the 
convoluted  tubes  may  possess  the  one  character,  while 
others  represent  the  other  variety. 

4.  Gastric  glands. — In  the  stomach  are  two  varieties 
of  compound  tubular  glands,  which  possess  an  epithe- 
lial lining  presenting  peculiarities  somewhat  different 
from  the  preceding. 

In  looking  at  the  mucous  surface  of  the  stomach 
with  a  good  magnifying  hand-lens,  immense  numbers 
of  minute  holes  can  be  seen.  They  are  generally 
collected  together  in  groups  of  three  to  five  or  more. 
These  small  holes  are  orifices  of  the  ducts  of  glands 
occupying  the  thickness  of  the  mucosa.  They  have 
been  called  peptic  (/lands.  They  are  constructed  upon 
the  model  of  the  compound  tubular  gland.  They 
consist  of  a  common  duct  with  a  wide  lumen.  The 
surface  of  the  mucous  membrane  of  the  stomach  is 
covered  by  a  single  layer  of  columnar  epithelia. 
During  digestion  many  of  these  cells  elaborate  and 
discharge  mucus,  and  in  doing  so  assume  the  form  of 
goblet-cells.  Columnar  cells,  identical  in  appearance 
with  those  of  the  mucous  surface,  line  in  a  single  layer 
the  walls  of  these  ducts.  Near  the  middle  of  the 
thickness  of  the  rete  mucosa  the  ducts  suddenly  narrow 
and  divide  into  two  or  more  smaller  branches,  which 
immediately  become  constricted,  to  form  the  nock  or 
intermediary  portion  of  the  secreting  tube.  The  neck 
of  the  secreting  tube  is  lined  by  a  continuation  of  the 
epithelium  in  the  duct,  but  the  cells  are  much  shorter. 
Immediately  outside  of  the  latter,  and  between  them 
and  the  basement-membrane,  are  scattered  here  and 
there  single  cells  of  a  very  granular  aspect  containing 


a  round  or  oval  nucleus,  both  cell  and  nucleus  being 
more  or  less  flattened.  They  consist  of  an  intra-cellu- 
lar  and  an  intra-nuclear  network,  and  have  been  called 
by  some  authors  peptic  cells  (Figs.  17,  18).  They  do 

Fig.  17. 


PEPTIC  GASTRIC  GLANDS. — a.  Com- 
mon duct.     6,  b.   Its  chief  branches. 


PORTION  OF  ONE  OF  THE  C^CJE  OF  A 
PEPTIC  GASTRIC  GI.AND  MOKE  HIGHLY 
MAGNIFIED:  seen  longitudinally  at  A  ; 
transversely  at  B.  a.  Basement-mem- 
brane. &.  Large  glandular  or  peptic 


c.  Terminal  Cffica  with  spheroidal  cell.  c.  Small  epithelial  cells  sur- 
gland  or  peptic  cells.  (Carpenter.)  rounding  the  lumen.  (Carpenter.) 

not  constitute  a  continuous  layer.  They  are  more 
closely  aggregated  in  the  neck  and  upper  portion  of 
the  secreting  tube  than  towards  the  fundus,  although 
they  are  also  present  in  the  deepest  end  of  the  tube. 
The  secreting  tubes  into  which  the  large  duct  divides 
are  somewhat  wavy  in  their  course.  They  are  often 
quite  curved  at  their  csecal  extremities.  After  the 
constriction  of  the  neck  they  gradually  increase  in 
diameter  until  the  deep  end  of  the  tube  is  reached. 
As  the  tube  widens  the  lining  epithelium  lengthens, 
still,  however,  leaving  a  distinct  lumen  for  the  passage 
of  the  mucous  secretion.  The  cells  of  the  fundus 
contain  a  spherical  nucleus  in  the  outer  end  of  the 
cell,  and  an  intra-cellular  and  intra-nuclcar  network 
whose  meshes  do  not,  however,  present  a  linear  ar- 
rangement such  as  is  seen  in  the  cells  which  line  the 
neck  of  the  secreting  tubes  and  the  common  duct. 
Between  the  epithelia  upon  the  surface  of  the  gastric 
mucous  membrane  is  a  scant  reticulurn  of  branched 
connective-tissue  or  endothelial  cells.  Similar  cell$, 
and  their  processes  also  penetrate  the  intercellular 
cement  of  the  whole  epithelial  lining  of  the  peptic 
glands. 


EPITHELIUM. 


43 


Fig.  19. 


ISOLATED  HEPATIC  CELLS. — a,  &, 
Normal,  but  b  more  highly  mag- 
nified, showing  the  nucleus  and 
distinct  oil-particles ;  c,  cells  in 
various  stages  of  fatty  degeneration. 
(Carpenter.) 


Liver-  and  kidney -cells. — The  gland  cells  of  the  liver 
possess  one,  sometimes  two  spherical  vesicular  nuclei 
with  an  investing  membrane  of  double  contour  and 
an  intra-cellular  and  intra-  » 

nuclear  network.  The  net- 
work appears  to  be  ar- 
ranged somewhat  as  a 
honeycomb.  In  the  spaces 
of  this  honeycomb  are 
drops  of  fat,  with  biliary 
granules,  and  occasionally 
pigment.  The  cells  are 
polyhedral  from  mutual 
pressure,  their  outlines 
generally  presenting  five 
or  six  sides.  They  are 
soft,  rnembraneless,  and  ap- 
parently granular. 

The  cells  lining  the 
tubules  of  the  kidneys  pre- 
sent diverse  aspects  accord- 
ing to  the  relative  portion  of  the  tubules  in  which 
they  are  located.  Those  in  the  convoluted  por- 
tions of  the  tubes  are  more  or  less  granular  and 
opaque.  Here  they  are  mernbraneless,  and  each  con- 
tains a  round  or  slightly  oval  nucleus  a  little  towards 
the  deep  part  of  the  cell.  The  cells  are  more  or  less 
cubical  in  form  with  a  tendency  to  a  columnar  shape. 
They  are  longitudinally  striated — an  appearance  due 
to  the  presence  of  large  numbers  of  minute  rod-like 
fibres  with  a  general  direction  perpendicular  to  the 
axis  of  the  tube.  These  minute  rods  or  fibres  are 
in  truth  united  into  a  network,  the  meshes  of  which 
are  extremely  long  and  narrow.  The  nucleus  also 
contains  a  network. 

Glands  of  the  skin. — 1.  Sweat-glands.  The  sudori- 
parous glands  of  the  cutaneous  surface  are  simple  tubes 
which  at  their  deep  portions  are  very  much  convo- 
luted. In  the  straight  portion  of  each  tube,  as  it  passes 
through  the  derma,  there  is  an  epithelial  lining  con- 
sisting of  a  single  layer  of  more  or  less  cubical  or  short 
columnar  cells.  These  cells  contain  a  nucleus,  and  are 
more  or  less  longitudinally  striated— an  appearance 
due  to  the  presence  of  an  intra-cellular  and  intra- 
nuclear network,  the  prevalent  direction  of  whose 
fibrillae  is  longitudinal.  In  the  convoluted  portion 
the  epithelial  cells  are  much  less  striated,  because 
the  meshes  of  the  reticulum  of  which  they  are  in 
part  composed  are  much  more  irregularly  arranged. 

2.  Sebaceous  (/lands. — The  sebaceous  glands  consist 
of  two  or  more  lobules  attached  to  an  excretory  duct. 
The  lobules  are  as  a  rule  regular,  ampullar  dilata- 


tions, lined  with  two  or  more  layers  of  epithelial  cells. 
The  peripheral  layer  of  cells  rests  upon  the  basement- 
membrane,  and  consists  of  cubical  epithelia  having 
spherical  or  flattened  nuclei  containing  one  or  more 
nucleoli.  These  cells  are  more  or  less  granular — an 
appearance  due  in  part  to  the  presence  of  a  fine  reti- 
culum in  the  cell-body  and  nucleus,  and  also  in  part 
to  the  presence  in  the  meshes  of  this  reticulum  of 
small  fatty  particles.  The  second  layer  of  elements  is 
composed  in  the  main  of  cells  similar  to  those  of  the 
outermost  layer,  which  have  undergone  a  metamor- 
phosis into  fat- vesicles.  The  molecules  of  fat,  which 
are  at  first  scattered  through  the  meshes  of  the  reti- 
culum, accumulate  so  rapidly  that  thev  distend  its 
meshes  inordinately,  and  finally  cause  the  atrophy 
and  destruction  of  the  nucleus  and  the  breaking- 
down  of  the  fibres  of  the  reticulum.  The  small  fatty 
particles  then  run  together  and  form  a  large  fat-drop, 
which  ultimately  bursts  its  protoplasmic  envelope 
and  becomes  free  in  the  lumen  of  the  gland. 

Hair  and  hair-follicles. — Epithelium  enters  into 
the  construction  of  the  shaft  and  the  sheath  of  hair — 
structures  met  with  very  extensively  on  the  surface 
of  the  body.  The  hair-follicle  begins  its  development 
in  the  skin  as  early  as  the  third  or  fourth  month  of 
the  existence  of  the  foetus.  The  first  stages  of  de- 
velopment are  exactly  similar  to  those  of  the  sweat- 
gland.  Both  these  organs  arise  by  an  ingrowth  of 
the  cutaneous  epithelium,  in  the  shape  of  buds,  which 
rapidly  extend  in  length,  burrowing  their  way  into 
the  depth  of  the  connnective-tissue;  for  some  time 
after  development  has  begun,  it  is  impossible  to  say 
whether  a  certain  epithelial  bud,  growing  into  the 
connective-tissue,  will  ultimately  form  a  sweat-gland 
or  a  hair-follicle.  After  the  epithelial  bud  has  thus 
entered  some  distance,  the  mass  presents  the  first 
characteristic  indication  of  the  formation  of  a  hair, 
by  a  more  or  less  definite  appearance  of  two  layers: 
viz.,  an  axial  and  a  peripheral  layer,  or  the  true  hair 
and  its  investing  sheath.  By  further  evolution  these 
two  portions,  into  which  the  mass  of  cells  filling  the 
depression  in  the  derma  has  separated,  subsequently 
develop,  the  axial  portion  into  the  shaft,  the  peripheral 
portion  into  the  sheath  of  the  hair.  After  this  stage 
of  growth  has  been  reached,  the  space  thus  channelled 
out  of  the  connective- tissue,  and  filled  with  the  sheath 
and  shaft  of  the  hair,  receives  definitely  the  name  of 
hair-follicle.  The  adult  hair  follicle  normally  contains 
epithelial  elements  very  similar  to  those  of  the  com- 
mon epidermis,  but  presenting  some  characteristics  of 
form  and  arrangement  which  are  peculiar  to  the  hairs. 
Since  the  hair-follicle,  sheath,  and  shaft  are  formed  by 


44 


HISTOLOGY. 


an  infolding  of  cutaneous  surface,  the  arrangement  of 
the  various  elements  is  essentially  the  same  as  upon 
the  surface  of  the  skin.  The  sheath  of  the  hair  is 
composed  of  an  inner  and  an  outer  portion.  The  outer 
portion  is  a  continuation  of  the  rete  inucosum  of  the 
skin,  and  consists  of  epithelial  cells  identical  in  struc- 
ture and  arrangement  with  those  of  the  normal  rete 
mucosurn  (b,  fig.  1,  Plate  II.).  Interspersed  among 
these  epithelia  is  a  small  number  of  branched  proto- 
plasmic cells,  in  every  way  similar  to  those  upon  the 
surface  of  the  derma.  Internal  to  the  cells  correspond- 
ing to  the  rete  mucosum  of  the  skin  is  the  inner 
sheath  (c,  fig.  2,  Plate  II.).  It  is  composed  of  two 
strata  of  transparent  cells,  the  innermost  stratum 
containing  elements  with  a  visible  nucleus.  Both  cell 
and  nucleus  are  somewhat  ovoid  in  shape,  while  the 
cells  of  the  outermost  stratum  are  destitute  of  nuclei. 
The  latter  are,  perhaps,  a  continuation  of  the  cells  of 
the  stratum  granulosum  of  the  surface,  although  they 
contain  no  granules.  Within  the  innermost  sheath, 
is  the  axial  shaft  or  hair  proper,  itself  covered  with  a 
very  thin  cuticle  (e,  fig.  2,  Plate  II.).  The  cuticle 
consists  of  a  single  imbricated  layer  of  thin  epithelial 
scales  without  visible  nuclei  (c,  fig.  1,  Plate  II.).  The 
hair-shaft  comprises  two  portions  when  seen  trans- 
versely, viz.,  a  cortical  cylinder  and  a  medullary  axis. 
With  its  investing  cuticle,  the  shaft,  except  in  and 
near  the  hair-bulb  at  the  root  of  the  hair,  consists 
entirely  of  extremely  thin  corneous  epithelial  scales 
without  a  vestige  of  nuclei.  They  are  so  densely 
packed  together,  that  it  is  impossible,  even  after 
mechanical  dissociation,  to  distinguish  the  outlines  of 
the  cells.  After  the  action  of  sulphuric  or  nitric  acid 
upon  them,  the  intercellular  cement-substance  is  dis- 
solved, when  the  thin  scales  can  be  readily  separated 
by  means  of  needles,  and  their  characters  demon- 
strated (fig.  <±,  Plate  II.).  The  corneous  cells  of  the 
shaft  represent,  therefore,  the  stratum  corneum  ot 
the  epidermis.  Some  of  the  minute  interstices  between 
the  corneous  scales  may  contain  particles  of  fatty 
matter  or  pigment-granules.  The  greater  or  lesser 
abundance  of  the  latter  determine  the  light  or  dark 
color  of  the  hair.  Some  of  these  minute  capillary 
spaces  may  contain  air.  When  many  of  them  are 
filled  with  air,  and  at  the  same  time  the  pigment  par- 
ticles, previously  mentioned,  are  present  only  in  small 
numbers  or  are  entirely  absent,  the  hair  presents  a 
glistening  silvery  'aspect.  The  medullary  or  axial 
portion  of  the  shaft  consists  of  an  irregular  aggrega- 
tion of  shrunken  epithelia  of  an  original  form  more  or 
less  polygonal.  These  shrunken  angular  cells  some- 
times contain  pigment-granules,  sometimes  minute 


vacuoles  filled  with  air,  and  the  same  gaseous  sub- 
stance generally  fills  the  interstices  between  the 
shrunken  cells.  The  medullary  axis  of  the  hair-shaft, 
no  matter  ^vhat  the  color  of  the  cortical  cylinder  may 
be,  shines  through  the  latter,  presenting  a  lighter  and 
more  glistening  appearance. 

The  foregoing  characters  of  the  hair  are  commonly 
observed  in  those  portions  above  the  bulb  or  root  of 
adult  hair.  As  the  bottom  of  the  follicle  is  reached, 
the  distinctions  between  the  inner  and  outer  sheath 
become  lost  in  the  general  embryonal  character  of  the 
epithelium.  The  hair-shaft  is  now  also  changed  both 
in  shape  and  in  the  character  of  the  constituent  ele- 
ments. It  expands  into  a  bulb-shaped  extremity  a 
little  above  the  bottom  of  the  follicle.  The  cuticle 
covering  this  lulb  is  composed  of  slightly  granular  epi- 
thelia  containing  distinct  nuclei.  At  the  bottom  of 
the  follicle  these  cells  are  more  or  less  spherical,  but 
they  flatten  and  their  size  and  the  distinctness  of  their 
nuclei  lessen  gradually  from  below  upwards,  as  can 
be  seen  by  reference  to  the  figure  already  indicated, 
until,  above  the  bulb,  the  nucleus  is  lost  entirely,  and 
the  cell  is  converted  into  the  thin  transparent  cuticu- 
lar  plates  or  scales  already  mentioned. 

The  two  portions  of  the  hair-shaft  also  present  in 
the  root  an  aspect  entirely  different  from  that  of  the 
outermost  end.  For  a  slight  distance  above  the  bulb 
the  cells  of  the  cortical  cylinder  are  less  corneous  and 
they  contain  a  trace  of  a  nucleus.  As  the  bulb  is 
approached,  the  epithelia  of  this  cylinder  gradually 
increase  in  thickness,  while  their  nuclei  also  become 
larger  and  more  defined.  In  the  bulb  itself,  the  epi- 
thelial cells  present  the  characteristics  of  the  most 
superficial  cells  of  the  rete  mucosum. 

A  vascular  connective-tissue  papilla  springs  from 
the  bottom  of  the  hair-follicle  and  penetrates  the 
centre  of  the  hair-bulb.  On  the  sides,  it  is  ensheathed 
by  the  cellular  accumulation  which  is  continuous 
above  with  the  corneous  cortical  cylinder  of  the  hair- 
shaft.  Above  this  papilla  is  a  mass  of  epithelial  cells, 
similar  to  those  of  the  cortical  part  of  the  bulb,  which 
is  continuous  with  the  shrunken  irregular  corneous 
cells  of  the  medulla  or  axis  of  the  shaft.  These 
medullary  cells  of  the  bulb  pass  by  slow  gradations 
from  below  upwards  into  the  irregular  corneous  cells 
already  described  as  existing  in  the  axis  of  the  hair, 
but  they  still  present  distinct  nuclei  at  a  level  much 
higher  than  that  of  the  bulb.  The  papilla  seems  to 
be  the  main  source  of  the  vitality  and  growth  of 
the  hair. 

Destruction  and  regeneration  of  epithelium.  —  The 
various  investing  epithelia,  of  the  cutaneous  surfaces 


THE    CONNECTIVE-TISSUE    SYSTEM. 


45 


and  of  the  mucous  surfaces  as  well,  seem  to  undergo 
a  constant  destruction  and  regeneration.  Desquarna- 
tion  is  constant  upon  the  external  surfaces,  and  it 
seems  also  to  be  a  common  although  less  rapidly 
occurring  phenomenon  upon  the  mucous  surfaces. 
This  constant  loss  of  cells  must  be  fully  compen- 
sated by  an  active  new  formation  of  elements.  It  is 
generally  conceded  that  the  new  supply  of  cells  must 
come  from  the  layer  corresponding  to  the  rete  muco- 
suin  in  the  stratified  epithelial  coverings.  Whether 
these  new  cells  are  produced  by  a  proliferation  of 
the  soft  finely  granular  polyhedral  epithelial  cells 
of  the  rete  mucosum,  or  whether  they  arise  from 
the  wandering  cells  which  are  always  present  in 
greater  or  lesser  numbers  in  the  epithelial  coverings, 
or  whether  they  are  in  part  derived  in  both  ways,  in- 
vestigators have  not  entirely  determined.  Many  up- 
hold one  of  ih.3  extreme  opinions,  while  some  defend 
the  middle  ground. 

It  is  quite  certain  that  under  the  influence  of  irri- 
tation not  only  do  the  rete  cells  proliferate,  but  even 
those  which  have  begun  to  approach  the  corneous 
condition  return  to  the  embryonal  state,  or  exhibit 
other  evidences  of  an  awakened  formative  power. 
Under  such  a  stimulus,  some  of  the  cells  may  contain 
an  endogenous  progeny.  Such  a  condition  is  fre- 
quently met  with  in  and  around  tumors,  and  upon 
epithelial  surfaces  secreting  pus. 

The  regeneration  upon  granulating  surfaces  of  epi- 
thelium, or  its  new  formation  over  abrasions,  seems  in 
some  way  to  be  more  or  less  closely  related  to  the 
action  of  previously  existing  epithelial  cells.  The 
newly  formed  epithelium  is  almost  always  connected 
directly  with  the  old  epithelium  at  the  edges  of  the 
wound.  If  a  large  abraded  surface  be  sprinkled  freely 
with  epithelial  scales,  isolated  islands  of  newly  formed 
epithelia,  which  exhibit  no  direct  connection  with  the 
epithelium  at  the  edges,  may  after  some  time  make 
their  appearance. 

Skin-yraftinrj. — One  means  of  healing  extensive 
granulating  surfaces  is,  by  the  employment  of  skin- 
grafts.  This  method  is  in  some  respects  essentially 
identical  with  that  of  dusting  the  surface  with  epithe- 
lial scales.  In  both  instances,  the  presence  of  epithe- 
lium seems  to  affect  the  granulation-cells  in  a  peculiar 
manner,  and  cause  the  latter  to  develop  into  epithelia. 
There  seems  to  be  an  infection  of  the  granular  cells  by 
the  epithelia,  or,  so  to  speak,  an  "action  of  presence"  of 
the  epithelial  scales,  which  is  shown  in  the  tendency 
of  the  embryonal  cells  acted  upon  to  form  epithelium 
rather  than  connective-tissue. 


THE  CONNECTIVE-TISSUE  SYSTEM. 

Having  reviewed  some  of  the  numerous  cellular 
elements  which  in  part  constitute  the  human  organ- 
ism, we  now  enter  upon  the  consideration  of  the 
histological  relation  which  they  bear  to  other  consti- 
tuents. We  have  already  studied  the  lymph  and  the 
blood — tissues  which  from  their  derivation  may  be 
classed  as  congeners  of  connective-tissue. 

The  connective-tissue,  in  one  form  or  another,  be- 
sides special  offices  which  it  may  perform  in  the 
human  economy,  acts  as  the  framework  upon  which 
and  within  which  the  various  elements  and  organs 
are  supported.  Upon  it  rests  the  investing  epithe- 
lium. In  it  are  imbedded  the  glands,  the  muscles, 
the  vessels,  and  the  nerves. 

The  great  connective-tissue  system  comprises  the 
following  groups  of  tissue,  which  will  be  examined  in 
the  order  in  which  they  are  here  enumerated :  Mucous- 
Tissue;  Varieties  of  Connective-Tissue,  properly  so 
called  —  Cartilage,  Bone,  Dentine,  and  Cementurn; 
Muscle,  Nerve,  and  the  Connective-Tissue  exhibited 
in  the  Bloodvessels  and  Lymphatics. 

MUCOUS-  OR  GELATINOUS-TISSUE. 

In  the  human  adult  this  form  of  tissue  is  of  ex- 
tremely limited  distribution.  It  is  found  in  the 
vitreous  humor  of  the  eye,  and  perhaps  in  the  enamel- 
organ  of  the  teeth.  In  the  embryo  it  is  very  exten- 
sive. It  presents  two  general  varieties,  which  are 
distinguished  by  the  character  of  the  cellular  ele- 
ments, and  the  intercellular  substance  which  sur- 
rounds them. 

The  simplest  form  of  mucous-  or  gelatinous-tissue 
is  that  represented  by  the  vitreous  humor  of  the  eye. 
It  consists  of  a  transparent,  colorless,  gelatinous  semi- 
fluid substance,  which  contains  a  more  or  less  con- 
siderable quantity  of  mucin,  or  of  a  substance  which 
has  a  very  similar  reaction.  It  is  precipitated  by 
weak  acids  in  the  form  of  minute  granules,  which 
then  give  to  this  semifluid  ground-substance  under 
the  microscope  a  finely  granular  aspect  and  a  slight 
opacity  when  viewed  by  the  naked  eye.  Imbedded 
in  this  gelatinous  semifluid  ground-substance,  cellular 
elements  are  present  in  more  or  less  considerable 
numbers,  according  to  the  age  of  the  subject  and  the 
quiescent  state  of  the  tissue.  In  the  adult  they  are 
scattered  at  rare  intervals.  These  cells  are  lymphoid 
elements  of  more  or  less  spherical  or  oval  outline. 


HISTOLOGY. 


They  are  capable  of  limited  movements,  which, 
however,  are  perhaps  not  usually  sufficient  for  loco- 
motion, although  some  of  them  are  doubtless  wander- 
ing cells.  They  have  no  limiting  membrane;  pos- 
sess one,  sometimes  two  or  more  nuclei,  and  consist 
of  an  intra-cellular  and  an  intra-nuolear  network, 
which  give  to  the  element  a  more  or  less  granular 
aspect.  The  ground-substance  seems  to  be  void  of 
bloodvessels  in  the  adult. 

Another  variety  of  mucous-tissue,  a  type  of  which 
is  met  with  in  the  Whartonian  jelly  of  the  umbilical 
cord,  has  a  more  complicated  structure,  and  is  a  grade 
higher  in  the  scale  of  development.  In  a  gelatinous 
mucin-containing  ground-substance  similar  to  that  of 
the  simplest  variety,  is  to  be  found  a  network,  or 
rather  felt-work  of  soft,  delicate,  slightly  refracting 
fibres.  These  are  collected  into  bundles  or  bands, 
sometimes  of  considerable  width.  Upon  and  near 
these  bundles,  cells  more  or  less  stellate,  and  in  other 
respects  similar  to  the  flat-branched  cells  of  loose 
connective-tissue  which  have  already  been  particu- 
larly described,  are  to  be  seen,  these  branches  form- 
ing by  their  communications  a  more  or  less  complete 
network  of  stellate  cells.  Some  of  the  bundles  con- 
tain, in  their  interior,  bloodvessels  with  distinct  and 
somewhat  thick  walls.  The  inter-fibrillar  areas  are 
also  sometimes  permeated  by  capillary  bloodvessels 
with  large  loose  meshes,  and  with  strong,  distinct 


walls.  These  capillary  vessels  are  ensheathed  by  a 
network  of  branched  cells.  The  intcrfibrillar  spaces 
also  contain,  in  small  numbers,  the  lymphoid  cells 
common  to  the  simplest  variety.  Sometimes  net- 
works, composed  of  fusiform  or  of  branched  connec- 
tive-tissue cells  (fig.  5,  Plate  II.),  are  seen  occupying 
the  inter-fibrillar  spaces.  In  some  pathological  for- 
mations of  mucous-tissue  there  is,  in  addition  to  the 
foregoing  structure,  a  sparse  network  of  fine  single 
elastic  fibres. 

WHITE  FIBROUS-TISSUE. 

Fibrous  bundles. — White  fibrous  connective-tissue 
is  most  extensive  in  its  distribution.  It  consists  of 
extremely  fine  fibrils  collected  together  into  bundles 
varying  widely  in  thickness  and  form.  These  bundles 
of  fibrils  may  be  cylindrical  or  band  like,  the  s'des  of 
the  cylinders  or  bands  being  usually  parallel.  The 
bundles  may  be  branched,  but  the  individual  fibres 
never  are  so.  The  course  of  the  bundles  may  be 
straight,  or  more  or  less  wavy,  according  to  whether 
they  are  tense  or  loose.  The  minute  fibrils  which 
constitute  the  bundles  are  united  and  held  together 
by  a  transparent  viscid  cement,  which  may  be  dis- 
solved by  weak  acids,  lime-water,  baryta  water,  10 
per  cent,  solution  of  salt,  and  by  other  means  known 
to  the  histologist.  In  some  locations,  the  bundles  are 


EXPLANATION  OF  PLATE  II. 


Fig.  1.    A  profile  view  of  a  Human  hair-follicle,  containing 

a  hair  under  a  high  power.  (After  Frey.) 
a,  The  fibrous  sheath  ;  b,  the  external  root  sheath  ;  c,  the 
cuticle  of  the  hair-shaft ;  p,  the  papilla  of  the  hair ;  h,  e, 
the  medullary  axis  of  the  hair-shaft ;  h,  the  cortical 
cylinder  of  the  hair-shaft ;  g,  the  transition  of  the  cor- 
neous epithelial  scales  of  the  cortical  cylinder  of  the  hair- 
shaft  above,  with  the  soft,  nucleated,  and  membrane- 
less  epithelium  of  the  bulbar  portion  of  the  hair ;  e,  point  of 
transition  of  the  soft  nucleated  epithelium  of  the  bulbar 
portion  of  the  medulla  of  the  hair-shaft  into  the  shrunkened, 
deformed,  and  dry  corneous  granules  which  fill  the  medulla 
of  the  upper  portion  of  the  shaft. 

Fig.  2.    Transverse  section  of  half  of  a  Human  hair,  with 

its  root  sheaths,  still  higher  power.     (After  Frey.) 
h,  Hair-shaft ;  e,  hair-cuticle  ;  c,  two  layers  of  the  internal 
root-sheath  ;  b,  external  root-sheath,  showing  an  outer  layer 
of  columnar  cells  ;  /,  basement  membrane  ;  a,  the  external 
fibrous  sheath. 


Fig.  3.  a,  b,  c,  Stellate  mucous-tissue  cells,  whose  processes 
form  a  more  or  less  complex  network.  (Moderate  en- 
largement.) 

Fig.   4.    Represents  isolated  cells  of  various  parts  of  the 

hair.  Highly  magnified.  (After  Frey.) 
e,  Nucleated  epithelial  cells  of  the  bulbar  portion  of  the 
hair ;  b,  h,  cells  from  the  cuticle  of  the  hair  ;  h',  corneous 
epithelial  cells  of  the  cortical  portion  of  the  shaft,  treated 
with  sulphuric  acid,  the  same  resolved  into  separate  plates 
at  A." 

Fig.  5.  Mucous  tissue  (gelatinous  tissue)  from  the  umbilical 
cord  of  a  Lamb,  very  highly  magnified.  (After  Kan- 
vie  r.) 

c,  Branched  cells  ;  n,  embryonal  cells,  or  lymph  corpuscles  ; 
F,  connective  fibres;  B,  intercellular  amorphous  fluid-sub- 
stance, containing  mucin. 


PLATE 


Fig.S. 


Fig. 4. 


THE   CONNECTIVE. TISSUE   SYSTEM. 


47 


more  or  less  completely  enveloped  in  a  thin  elastic 
sheath.  Such  ensheathed  bundles  are  to  be  found  in 
the  subcutaneous  connective-tissue,  in  the  subarach- 
noid  of  the  brain,  in  aponeuroses,  in  tendons,  and  in 
some  other  locations. 

Structure  and  arrangement  of  fibrous  bundles. — The 
bundles  of  fibrils  present  a  distinct  longitudinal 
fibrillation  when  seen  under  a  sufficient  magnifying 
power.  When  they  are  loose  and  wavy,  they  also 
appear  to  have  an  indistinct,  transverse  striation. 
Tins  is  an  optical  illusion  caused  by  short  and  very 
frequent  waves  in  the  course  of  the  fibrils.  This 
wavy  appearance  of  the  fibrils,  and  consequent  appa- 
rent transverse  striation,  may  be  seen  sometimes  even 
when  the  sides  of  the  bundle  seem  to  be  perfectly 
straight. 

Water  and  weak  acids  cause  the  interfibrillar  ce- 
ment to  swell,  and  give  the  bundle  a  hyaline  or 
homogeneous  aspect.  These  agents  have  no  such 
effect  upon  the  elastic  sheath  which  envelops  some  of 
the  bundles.  Ensheathed  bundles  appear  swollen  in 
some  places,  and  constricted  in  others,  thus  present- 
ing a  beaded  outline. 

The  bundles  of  fibrous  tissue  may  be  variously  ar- 
ranged with  respect  to  each  other.  The  simplest 
arrangement  is  that  of  a  collection  into  secondary 
bundles  or  bands,  which  run  parallel  with  each  other 
and  are  spread  out,  side  by  side,  to  form  lamellar 
membranes,  as  in  aponeuroses,  or  are  collected  to- 
gether to  form  rounded  cords,  as  in  tendons.  They 
may,  on  the  other  hand,  cross  each  other  in  various 
directions,  forming  a  loose  felt-work  with  wide  meshes, 
as  in  the  loose  connective- tissues ;  for  example,  the  sub- 
cutaneous- or  mucous-tissue,  the  inter-muscular  con- 
nective-tissue, the  loose  interstitial  connective-tissue  of 
glands,  etc.  Or  they  may  be  closely  packed  together 
to  form  a  very  dense  felt-work,  such  as  the  cutis, 
the  dura  mater,  etc. 

On  the  other  hand,  the  bundles  may  form  a  loose 
network  spread  out  in  the  form  of  a  membrane  with 
more  or  less  wide  meshes,  like  the  mesentery,  the 
ligamentum  dentatum  of  the  spinal  cord,  etc. 

Interfibrous  spaces,  and  their  cellular  contents. — The 
spaces  left  between  the  fibrous  bundles  are  conse- 
quently of  forms  varying  according  to  the  direction 
of  the  bundles.  They  are  filled  with  lymph,  and  con- 
stitute the  radicals  of  the  great  lymphatic  system. 

In  tendons,  the  spaces  left  between  the  bundles  are 
more  or  less  linear  when  viewed  longitudinally,  and 
when  seen  in  transverse  section  appear  more  or  less 
stellate. 

When  speaking  of  cndothelia  and  connective-tissue 


corpuscles,  we  described  the  flat  elastic  cells  which 
form  a  partial  lining  of  the  lymph-space  formed 
between  adjacent  parallel  bundles  of  tendons,  and 
stated  their  relation  to  the  bundles  of  fibrils  upon 
which  they  were  more  or  less  closely  applied.  It 
was  then  stated  that  these  cells  (the  flat  tendon-plates 
of  Eanvier)  spread  across  two  or  more  bundles.  Fig. 
2,  Plate  III.,  shows  very  beautifully  this  peculiar 
arrangement  of  the  tendon-cells.  The  drawing  re- 
presents a  number  of  (primary)  bundles  united  to- 
gether into  a  (secondary)  larger  bundle  forming  a 
small  tendinous  cord  in  the  tail  of  a  young  rat.  In 
larger  tendons  we  have  a  number  of  such  secondary 
bundles  collected  together  to  form  the  tendon.  Ten- 
dons of  this  kind  have  their  external  surface  covered 
by  a  complete  layer  of  large  flat  endothelial  plates 
such  as  line  serous  cavities,  which  rest  upon  an  ex- 
tremely thin  elastic  apparently  structureless  mem- 
brane. Such  a  tendon,  after  proper  treatment  by  ni- 
trate of  silver,  when  placed  under  the  microscope  and 
seen  longitudinally,  shows  this  superficial  covering 
of  endothelial  cells.  By  lowering  the  focus  the  flat 
tendon-cells  of  Eanvier  next  come  into  view.  The  lat- 
ter if  seen  in  surface  present  the  appearances  already 
described  Apropos  of  the  cells  of  the  connective-tissue. 
If  their  position  upon  the  secondary  bundles  is  such 
that  they  are  seen  in  profile,  they  then  appear  as  lines 
or  spindles  with  slightly  projecting  bellies  correspond- 
ing to  the  location  of  the  nucleus.  When  a  tendon 
composed  of  secondary  bundles  is  cut  transversely, 
and  properly  stained,  it  presents  a  number  of  more  or 
less  markedly  stellate  bodies  (Fig.  20)  connected  the 

Fig.  20. 


TRANSVERSE  SECTION  op  TENDON:  showing  so-called  branched  corpuscles, 
inclosing  spaces  which,  loft  bluuk,  are  naturally  filled  with  tendinous  fasci- 
culi, nigh  power.  (Carpenter.) 

one  with  the  other  by  anastomosing  branches  (C,  fig.  2, 
Plate  III.).  These  bodies  were  formerly  regarded  as 
stellate  connective  corpuscles.  They  are,  in  normal 
tendon,  generally  nothing  more  than  the  cross  cuts  of 
the  more  or  less  flat  tendon  plates  of  Ranvier.  These 
stellate  forms  may  consist  of  two  or  more  of  such  plates 
in  apposition.  Sometimes  even  one  or  more  lymphoid 


43 


HISTOLOGY. 


cells  may  be  mingled  with  them.  They  may  thus  be 
formed  of  aggregations  of  cells,  in  which  case  several 
nuclei  may  be  visible  within  them.  The  anastomosing 
branches  appear  to  be  sections  of  the  primary  or 
secondary  cell-plates  and  their  lateral  ramifications. 
The  clear  spaces  constituting  the  meshes  formed  by 
the  previously  mentioned  anastomoses  correspond  to 
transverse  sections  of  bundles  of  fibrils  which  have 
not  taken  the  staining. 

Besides  the  fixed  cells  above  described,  leucocytes 
or  wandering  cells  are  found  in  small  numbers  in  the 
lymph  spaces  of  the  connective- tissue. 

Elastic  fibres. — When  tendons  are  thoroughly  boiled 
the  white  fibrous  tissue  which  constitutes  them  is  dis- 
solved, and  the  other  elements  previously  mentioned 
disappear.  The  more  complete  this  effect  of  boiling, 
the  more  visible  becomes  a  network  formed  of  single 
highly  refracting  elastic  fibres.  These  elastic  fibres 
are  very  small  in  diameter,  are  more  or  less  perfectly 
cylindrical,  are  branched  at  intervals,  and  are  appa- 
rently homogeneous. 

Their  branches  unite  to  form  a  network,  whose 
meshes  are  long  and  narrow,  the  long  diameter  of  the 
meshes  being  parallel  with  the  axis  of  the  tendon 
bundles  which  they  accompany.  These  elastic  fibres 
are  in  contact  with  the  sheath  which  envelops  the  pri- 
mary bundles  more  or  less  completely.  They  are  so 
difficult  to  be  seen  that  unless  they  are  specially  pre- 
pared they  are  generally  invisible. 

In  aponeuroses,  where  the  fibrous  bundles  are 
arranged  so  as  to  form  thin  lamellae  of  considerable 
width,  the  fibres  of  a  given  lamella  run  parallel  with 
each  other,  and  are  crossed  at  an  angle  by  those  of 
the  lamella  next  above  or  below.  In  many  such 
lamellar  fibrous-tissues,  the  fibres  in  adjoining  lamellae 
cross  at  right  angles.  The  tendon-cells  are  then 
found  to  be  much  more  irregularly  formed  than  in 
the  simplest  variety  of  tendon.  In  the  adult  these 
cells  are  not  so  frequently  arranged  in  rows  as  in  the 
simple  tendons,  and  the  secondary  plates  which  spring 
from  the  body  of  the  cell  may  then  have  a  direction 
corresponding  to  that  of  the  different  fibrous  bundles 
with  which  they  are  in  contact. 

Loose  connective-tissue. — In  the  loose  connective-tis- 
sue, for  example  the  subcutaneous  cellular-tissue  so 
called,  the  bundles  of  fibrils  run  in  every  conceivable 
direction,  sometimes  branching  and  forming  frequent 
anastomoses.  The  spaces  left  between  the  fibrous 
bundles  are  generally  large,  and  they  freely  inter- 
communicate. Fluid  or  air  injected  into  them  readily 
passes  from  one  to  another.  After  having  been  dis- 
tended by  air  and  dried,  they  present  the  appearance 


to  the  naked  eye  of  large  cells  or  vesicles,  hence  the 
name  of  cellular- tissue.  Some  of  the  bundles  of  fibres 
are  ensheathed  as  already  mentioned,  many  of  them 
are  not.  The  fixed  cells  of  the  connective-tissue  are 
not  very  numerous  in  adult  tissue  of  this  kind.  They 
are  loosely  applied  to  the  surface  of  one  or  more 
bundles,  frequently  at  their  points  of  crossing  (see 
fig.  3,  PI.  IX).  The  wandering  lymphoid  cells  are 
much  more  numerous  in  this  form  of  connective-tissue 
than  in  the  tendons  or  aponeuroses. 

Yellow  elastic  fibres  are  also  to  be  met  with. 
Here  they  are  frequently  much  larger  than  in  tendon, 
but  they  bear  much  the  same  relations  to  the  fibrous 
bundles  in  the  one  case  as  in  the  other.  The  larger 
elastic  fibres  have  been  found  by  some  investigators 
to  be  enveloped  by  a  thin,  dense  membrane,  which 
in  most  locations  is  extremely  difficult  to  demonstrate. 
In  the  loose  subarachnoid  connective-tissues  of  the 
brain,  and  in  some  other  locations,  this  investing 
sheath  is  quite  distinct. 

This  variety  of  fibrous  tissue  may  exist  in  the  form 
of  a  thin,  fenestrated  membrane.  Some  portions  of  the 
omentum  furnish  an  example  of  such,  the  fenestrag  in 
this  case  representing  the  dilated  lymph-spaces  exist- 
ing between  the  bundles  of  fibrous  tissue.  It  is  thought 
by  some  authors  (Axel  Key  and  Retzius)  that  many 
of  the  loose  connective-tissues  are  composed  of  scant 
felt-works  of  fibrous  bundles  spread  out  in  many 
superimposed  Iamel]a3,  which  are  more  or  less  sepa- 
rated from  each  other  by  a  single  layer  of  flat  endo- 
thelial  cells  resting  upon  one  side  of  an  extremely 
thin,  structureless  elastic  membrane. 

Dense  connective-tissue. — The  dense  fults  of -white 
fibrous  tissue,  as,  for  example,  those  of  the  true  skin, 
of  the  dura  mater,  etc.,  are  essentially  identical  in 
structure  to  the  loose  felts  of  the  subcutaneous  con- 
nective-tissue, of  the  submucous-tissue,  and  of  the 
interstitial  connective-tissue  of  muscles,  and  of  glands. 
The  fibrous  bundles  being  now  much  more  closely 
packed  together,  the  lymph-spaces  are  consequently 
smaller.  The  cellular  elements  are  also  present  in 
much  smaller  numbers. 

Bloodvessels. — The  bloodvessels  supplying  this  form 
of  connective-tissue  have  much  the  same  character 
as  in  the  fibrous  variety  of  mucous  or  gelatinous- 
tissue  already  described. 

There  are  two  other  varieties  of  white  fibrous  con- 
nective-tissue, namely,  the  neuroglia  and  the  reticular, 
or  lymphoid  tissue,  which  will  be  briefly  considered 
when  we  study  respectively  the  nervous  system  and 
the  lymphatic  system. 


TIIE    CONNECTIVE-TISSUE    SYSTEM. 


49 


YELLOW  ELASTIC-TISSUE. 

Another  form  of  connective-tissue  presents  itself  in 
the  yellow  elastic-tissue.  The  fibres  or  bands  com- 
posing it  differ  in  chemical  constitution  from  those 
of  white  fibrous  tissue.  They  are  not  influenced  by 
the  action  of  water,  weak  acid,  or  strong  alkalies. 
Unlike  the  white  fibrous  tissue,  the  individual  elastic 
fibres  frequently  branch,  and  by  the  anastomoses  of 
those  branches  form  a  genuine  network  with  meshes, 
varying  in  size  and  shape  according  to  the  location 
and  the  variety  of  elastic-tissue. 

Fine  elastic  fibres. —Ks  already  indicated,  every  form 
of  white  fibrous  tissue  contains  a  variable  amount 
of  elastic  tissue  in  one  form  or  another. 

Perhaps  the  simplest  and  most  widely  distributed 
variety  of  yellow  elastic-tissue  is  that  which  is  present 
among  the  bundles  of  white  fibrous  tissue  in  the  form 
of  a  loose  sparse  network  of  fine  cylindrical  apparently 
homogeneous  and  highly  refracting  fibres.  These 
fine  elastic  fibres  lie  in  close  proximity  to  the  (pri- 
mary) white  fibrous  bundles,  never  within  them. 
After  nearly  every  method  of  preparation  they  seem 
homogeneous,  presenting  no  trace  of  fibrillation  or 
other  structure.  But  when  freshly  submitted  to  the 
action  of  osmic  acid,  and  examined  under  a  mode- 
rately high  magnifying  power,  they  appear  trans- 
versely striated.  If  a  power  of  eight  or  niiie  hundred 
diameters  with  a  good  lens  is  employed,  the  transverse 
strias  are  resolved  into  highly  refracting  lenticular  or 
somewhat  spherical  forms,  imbedded  in  a  less  dense, 
hyaline,  transparent  substance. 

The  fibres  of  elastic-tissue  are  straight  or  curved 
according  to  the  tense  or  loose  condition  of  the  tissue 
in  which  they  are  found.  When  broken  they  curl 
up  at  the  extremity.  This  form  of  elastic  fibres  is 
met  with  also  in  the  matrix  of  yellow  elastic  cartilage. 

Coarse  elastic  fibres. — Besides  the  network  formed  of 
such  delicate  elastic  fibres  just  described,  many  white 
fibrous  tissues  contain  an  elastic  plexus,  composed  of 
much  coarser  fibres.  These  coarser,  elastic  fibres  are 
cylindrical  or  band-like.  Schwalbe  proved  them  to 
be  covered  by  a  delicate  elastic  sheath,  which  is  ordi- 
narily invisible.  After  the  action  of  osmic  acid  upon 
perfectly  fresh  specimens,  the  coarse  fibres  are  also  seen 
to  possess  the  peculiarity  of  structure  already  de- 
scribed for  the  finer  fibres.  This  variety  of  yellow 
elastic  fibres  is  also  met  with  in  the  skin  and  other 
felt- works  of  white  fibrous  tissues.  In  the  superficial 
portion  of  the  trachea  and  bronchi  they  are  closely 
packed  together  to  form,  with  but  a  sparse  amount 

of  interstitial  white   fibrous   tissue,  a   dense   lon<-i- 

o 

7 


tudinal  layer.  The  most  marked  development  of 
this  form  of  yellow  elastic-tissue  is  found  in  the 
ligamentum  nuchaj  and  the  ligamenta  subflava,  which 
may  be  regarded  as,  par  excellence,  types  of  yellow 
elastic  tissue.  Even  in  these  two  locations  there  is 
always  a  certain  quantity  of  white  fibrous  bundles 

Fig.  21. 


YELLOW  ELASTIC-TISSUE. — High  power.     (Gray.) 

scattered  through  the  meshes  formed  by  the  large 
yellow  fibres,  and  there  are  also  a  small  number  of 
the  formative  connective-tissue  cells  present.  The 
latter  bear  their  customary  relations  to  the  lymph- 
spaces  and  the  fibres.  In  this  tissue  the  elastic  fibres 
pursue  mainly  a  longitudinal  course,  and  are  closely 
applied  to  each  other.  But  if  thin  sections  are  made, 
and  pulled  out  laterally  by  needles,  it  is  easily  seen 
that  they  really  constitute  a  network.  This  form  of 
yellow  elastic-tissue  is  also  found  well  developed  in 
the  walls  of  large  arteries  and  veins. 

The  elastic  networks  heretofore  considered  are 
more  or  less  sponge-like  in  their  arrangement.  There 
are  elastic  fibres  which  are  band-like  and  in  some 
locations  form  only  lateral  anastomoses.  In  this  case 
we  have  an  elastic  fenestrated  membrane,  such  as  is 
present  in  the  inner  and  middle  coats  of  arteries  and 
veins  (see  fig.  3,  Plate  III.). 

Furthermore,  instead  of  a  fenestrated  membrane, 
we  may  have  a  continuous  layer  of  yellow  elastic- 


50 


HISTOLOGY. 


tissue  such  as  is  found  upon  the  posterior  surface  of 
the  cornea,  and  upon  the  surface  of  serous  cavities 
immediately  beueath  the  endothelia.  The  former 
membrane  (membrane  of  Descemef),  however,  is  known 
to  be  somewhat  fibrillar  in  structure,  although  ordi- 
narily it  does  not  appear  so. 

The  more  or  less  distinct  basement- membrane  of 
gland-tubes,  as  has  been  already  hinted,  is  an  elastic 
membrane  formed  sometimes  entirely  of  flat,  poly- 
gonal or  branched,  elastic  endothelial  plates. 

ADIPOSE    TISSUE. 

This  is  another  member  of  the  group  of  connective- 
tissues.  It  may  be  present  in  a  diffuse  manner  in  the 
subcutaneous  and  submucous  tissues  of  the  economy. 
In  the  well-nourished  it  is  frequently  present  in  the 
interstitial  connective-tissue  of  muscles  and  of  some 
glands,  and  it  may  be  found  in  greater  or  lesser  quan- 
tity in  subserous  connective-tissues.  Fatty  or  adipose 
tissue,  however,  is  usually  found  aggregated  into 
lobules,  each  one  of  which  generally  has  its  own  spe- 
cial vascular  apparatus,  being  supplied  by  an  afferent 
artery,  one  or  more  afferent  veins,  and  an  interme- 
diary capillary  network  of  small  meshes,  in  which 
one  or  two  adipose  cells  lay  (Fig.  22).  The  aggregation 

Fig.  22. 


BLOODVESSELS  OF  FAT. — 1.  Minute  flattened  fat-lobule,  in  which  the  vessels 
only  are  represented.  3.  Terminal  artery.  4.  Primitive  vein.  5.  Fat-cells  of  one 
border  of  the  globule  separately  represented.  (Magnified  100  diameters.)  2. 
Plan  of  arrangement  of  capillaries  on  exterior  of  fat-cells,  more  highly 
magnified.  (Gray.) 

of  the  cells  into  lobules,  the  possession  by  each  one  of 
these  lobules  of  its  own  vascular  supply,  and  a  mode 
of  development  which  is  similar  to  that  of  some  lymph- 
glands,  have  suggested  to  some  histologists  a  com- 
parison of  this  tissue  with  that  of  secreting  glands. 
Klein,  Creighton,  and  others  consider  the  lobules  of 
adipose  tissue  essentially  acini  of  ductless  glands. 


However  true  or  false  this  assumed  analogy  may  be 
in  fact,  there  is  undoubtedly,  up  to  a  certain  point, 
a  wonderful  parallelism  in  a  common  method  of  de- 
velopment for  the  adipose  lobule  and  the  lymph- 
follicle. 

Development  and  growth  of  adipose  tit  sue. — Accord- 
ing to  Klein,  and  some  other  accomplished  investi- 
gators, the  origin  and  growth  of  a  lobule  of  fatty 
tissue  in  the  mesentery  may  be  briefly  sketched  as 
follows : — 

In  the  vicinity  of  an  artery  of  somewhat  consider- 
able size  a  small  spot  can  be  seen  with  the  microscope, 
in  which  the  following  conditions  are  present.  In 
the  lymph-spaces  the  flat,  fixed  cells  of  the  connective- 
tissue  are  undergoing  proliferation ;  considerable  num- 
bers of  lymphoid  cells  are  being  formed  by  division 
and  budding.  The  connective-tissue  septa  between 
neighboring  lymph-spaces,  in  which  the  cells  are 
proliferating,  become  gradually  thinned  until  there 
remains  only  a  delicate  reticulum,  in  the  meshes  of 
which  are  to  be  found  newly-formed  lymphoid  cells. 
In  other  words,  a  genuine  lymphatic  reticular-tissue 
is  in  process  of  formation.  The  spot  of  reticular- 
tissue  at  first  forms  at  some  distance  from  a  blood- 
capillary.  After  the  cellular  activity  has  somewhat 
progressed,  the  nearest  capillary  begins  to  send  out 
one  or  more  loops  towards  the  little  lymphoid  spot  or 
nodule.  One  arm  of  this  loop  subsequently  grows 
into  an  arteriole,  the  other  develops  into  a  venule ; 
the  middle  portion  sends  out  protoplasmic  branches 
to  ramify  in  the  minute  nodule  of  lymphoid  tissue. 
Tn"ese  protoplasmic  branches  become  hollowed  out, 
finally  constituting  a  capillary  network,  which  per- 
meates the  newly-formed  cellular  mass.  Often  stel- 
late protoplasmic  cells  in  the  depth  of  the  nodule 
have  no  direct  connection  with  the  walls  of  previ- 
ously formed  or  developing  capillaries,  but,  by  a  pro- 
cess of  vacuolation,  become  hollowed  out  and  finally 
united  with  the  capillaries  to  form  new  bloodvessels. 
In  this  manner  the  newly-formed  nodules,  after  the 
commencement  of  their  growth,  are  supplied  with 
newly-formed  bloodvessels.  Adjacent  spots  or  no- 
dules, by  spreading,  may  unite  together  to  form 
greater  or  lesser  areas  of  similar  newly-formed  cellular 
tissue  of  a  lymphoid  character.  At  this  stage  of  de- 
velopment we  have,  as  far  as  the  eye  can  tell,  genuine 
lymphatic  or  reticular-tissue,  such  as  is  seen  especially 
well-defined  in  the  mucosa  of  the  intestines.  These 
spots  in  the  mesentery  are  always  covered,  at  least 
on  one  surface,  with  a  layer  of  germinating  endothelia. 

It  is  after  this  that  the  adipose  tissue,  as  such, 
makes  its  first  appearance.  In  some  of  these  nodules 


CARTILAGE. 


51 


or  lobules,  to  use  a  better  term,  a  larger  or  smaller 
number  of  the  cells  begin  to  charge  themselves  with 
minute  molecules  of  oil — a  circumstance  which  causes 
them  to  become  extremely  granular  and  somewhat 
opaque.  These  minute  fatty  granules  subsequently 
coalesce  to  form  fewer  and  larger  fat-drops  which  now 
load  the  cell  in  varying  numbers.  These  fat- drops  in 
their  turn  increase  in  size  and  finally  run  together. 
At  this  stage  of  development  of  the  fat-cell  we  find 
the  element  consisting  of  a  cell-body  which  is  spread 
out  over  the  oil-globule  as  a  thin  shell  of  protoplasm. 
The  nucleus,  which  has  been  pushed  to  one  side  and 
much  flattened,  has  an  enveloping  membrane  of 
double  contour,  and  it  contains,  as  does  also  the  cell- 
body,  a  network  of  fine  fibres  holding  in  its  close 
meshes  a  small  amount  of  semifluid,  transparent,  struc- 
tureless substance.  The  fat  continues  to  accumulate 
in  the  cell  until  the  enveloping  protoplasmic  shell  is 
so  stretched  and  distended  that  the  only  visible  trace 
of  it  to  be  seen,  under  the  microscope,  is  in  the  form 
of  an  extremely  thin  limiting  membrane  surrounding 
the  oil-globule  when  the  latter  is  viewed  in  optical  sec- 
tion. This  membrane  is  a  little  thicker  at  one  side — 
a  single  indication  of  the  location  and  existence  of 
the  nucleus.  The  cell  is  now  known  as  the  adipose 
vesicle  (Fig.  23).  In  a  growing  lobule  of  adipose 

Fig.  23. 


ADIPOSB  TISSUE. - 


z,  Star-like  bodies,  from  crystallization  of  fatty  acids.    High 
power.     (Gray.) 


tissue  the  different  fat-cells  may  present  various 
stages  of  the  elaboration  of  fat.  In  a  fully-developed 
one,  however,  all,  or  nearly  all,  the  cells  present  the 
aspect  of  a  fully-developed  vesicle.  The  vesicles  rest 
in  the  meshes  of  the  rich  capillary  plexus  which  sur- 
rounds and  permeates  the  lobule.  At  the  periphery 
of  a  full-grown  lobule  a  small  amount  of  loose  fibrous 
bundles  may  be  seen  between  the  cells,  accompanied 
by  a  small  number  of  fixed  and  mobile  connective - 


tissue  corpuscles.  In  the  depth  of  the  lobule  this 
fibrous  framework  has  apparently  disappeared,  at  any 
rate  it  is  here  generally  invisible,  since  only  the  cap- 
illary vessels  are  to  be  seen. 

Whether  the  adipose  lobules  are  developed  in  the 
mesentery  or  in  the  subcutaneous,  submucous,  or 
interstitial  connective  tissues,  it  is  usually  after  the 
method  above  sketched :  First,  the  formation  of  a 
lymphoid  nodule ;  then,  the  supply  of  this  nodule  by 
a  special  newly-formed  vascular  system;  last,  the 
gradual  transformation  of  the  vascularized  lymphoid 
nodule  into  an  adipose  lobule. 

Diffuse  formation  of  fat. — There  is  also  a  not  infre- 
quent formation  of  diffused  adipose  tissue  in  the  sub- 
cutaneous, submucous,  and  intermuscular  loose  con- 
nective tissue  by  the  direct  infiltration  and  transform- 
ation into  adipose  vesicles,  of  the  fixed  and  other  cells 
already  existing  in  these  tissues.  Such  a  direct  trans- 
formation of  the  connective-tissue  cells  into  fat-vesi^es 
may  involve  wide  areas  of  tissue,  and  result  in  the 
formation  of  more  or  less  thick  and  extensive  strata 
of  adipose  tissue.  The  large  granular  plasmatic  cells 
of  Waldeyer,  which  are  usually  found  in  greatest 
numbers  in  the  neighborhood  of  vessels,  very  fre- 
quently experience  this  direct  transformation  or  infil- 
tration. 

In  this  latter  method  of  formation,  the  blood  vessels 
actively  increase,  for  adipose  tissue  is  pre-emi- 
nently a  vascular  tissue. 

The  fat  once  formed,  it  and  the  cell  contain- 
ing it  may  suffer  various  changes.  By  an  inter- 
ference with  the  vascular  supply  the  fat  may 
ultimately  decompose,  and  fat-crystals  form  in 
the  interior  of  the  vesicles.  Or,  on  the  other 
hand,  under  the  influence  of  an  increased  activity 
of  the  cell-irritation — in  inflammation  for  exam- 
ple— or  of  a  demand  for  nutritive  material,  sucli 
as  may  be  occasioned  by  inanition  or  fasting,  the 
fat  may  gradually  disappear,  leaving  in  its  place 
at  first  a  serous  fluid  which  still  distends  the  cell 
and  preserves  its  vesicular  form.  If  the  irritation 
or  the  demand  for  nutritive  material  still  continue,  this 
serous  fluid  gradually  disappears  and  the  cell  finally 
returns  to  the  original  form  it  possessed  before  the 
fat  first  made  its  appearance. 

CARTILAGE. 

In  cartilage  we  have  a  structure  which  has  been 
classed  with  the  various  forms  of  connective  tissue, 
but  there  seems  to  be  a  wide  variance  between  it  and 
other  groups  of  the  great  connective- tissue  system, 


52 


HISTOLOGY. 


both  as  to  its  chemical  constitution  and  its  intimate 
structure.  While  the  other  groups  of  the  connective- 
tissues  yield  gelatine  on  boiling,  the  cartilages,  on  the 
contrary,  yield  chondrin.  Cartilage  consists,  like  the 
other  tissues,  of  cells  and  intercellular  substance;  the 
latter  is  .now  known  as  the  ground  substance  or 
matrix.  There  are  three  principal  varieties  of  carti- 
lago  which  arc  distinguished  from  each  other  by 
variations  in  the  nature  of  the  matrix  rather  than  in 
the  cells.  These  principal  varieties  are  hyaline  carti- 
lage, reticular  or  yellow  elastic  cartilage,  and  white 
fibrous  cartilage. 

HYALINE  CARTILAGE. 

The  simplicity  of  the  structure  of  hyaline  cartilage 
is  nearly  equal  to  that  of  the  simplest  form  of  mucus 
or  gelatinous  tissue. 

Cartila'jn  cells. — The  cells  are  generally  more  or 
less  spherical  or  ovoid,  when  free  to  assume  shapes 
which  are  not  the  result  of  unequal  pressure.  They 
contain  one,  occasionally  two,  large  spherical  vesicu- 
lar nuclei  with  a  thin  limiting  membrane  of  double 
contour.  The  nucleus  may  contain  one  or  more  com- 
paratively large  and  distinct  nucleoli.  The  cell-body 
often  incloses  a  few  small  fat  drops  and  fatty  granules. 
The  nucleus  consists  of  a  network  of  fibrils  similar  to 
the  intra-nuclear  network  of  other  cells,  but  the  fibrils 


which  constitute,  with  a  semifluid  inter-fibrillar  sub- 
stance, the  body  of  the  cell,  instead  of  forming  a  true 
network  as  in  other  cells,  are  arranged  in  a  dense 
felt-work  with  the  fibres  crossing  each  other,  and 
interlacing  in  all  directions.  The  cartilage-cell  pos- 
sesses one  characteristic  which  unmistakably  distin- 
guishes it  from  other  cells,  and  marks  the  tissue  in 
which  it  is  formed  as  cartilaginous.  It  has  the  faculty 
of  causing  a  halo  to  be  formed  around  it  of  substance 
similar  to  the  matrix  of  hyaline  cartilage — a  more  or 
less  thin  film  known  as  the  capsule.  This  peculiarity 
of  the  cartilage  cell,  it  should  be  remarked  here  once 
for  all,  is  a  characteristic  of  all  cartilage-cells,  whether 
of  one  variety  of  cartilage  or  of  another.  The  carti- 
lage cell  is  capable  of  limited  movement.  It  can 
swallow  minute  particles  brought  directly  in  contact 
with  its  body,  and  under  the  stimulus  of  physiological 
growth,  or  of  pathological  irritation,  can  multiply  by 
division.  Under  the  influence  of  such  a  stimulus 
the  cell  first  enlarges ;  then  the  nucleus  divides  by 
fission  or  by  gemmation;  finally,  the  cell-body  suffers 
a  constriction  and  an  ultimate  division  into  new  cells, 
each  containing  a  micleus.  If  the  stimulus  is  ener- 
getic, each  new  cell  may  again  divide.  Thus  two, 
four,  eight,  or  even  sixteen  or  thirty-two  new  cells 
may  be  formed  as  the  progeny  of  the  original  cell. 
The  original  cell  has  been  termed  the  mother  cull, 


EXPLANATION  OF  PLATE  III. 


Fig.  1.  White  fibrous  connective-tissue,  highly  magnified. 

a,  The  fibrous  bundles ;  5,  nuclei  of  endothelial  cells  ap- 
plied to  the  surface  of  the  bundles,  or  of  stellate  connective- 
tissue  corpuscles  resting  in  the  interfibrous  lymph  spaces  ;  c, 
a  lymphatic  lacuna. 

Fig.  2.  A.  Highly  magnified  view  of  an  isolated  cord  of 
primary  bundles  of  white  fibrous  tissue  from  the  tail  of  a 
yo'ung  Rat.  Fresh  specimen,  silver-treated.  High  power. 

n,  Nucleus  of  flat  endothelial  cell-plate  applied  to  the  sur- 
face of  the  cord,  the  cell  is  seen  to  spread  across  two  or  more 
bundles ;  similar  endothelial  cells  are  arranged  in  a  row — 
they  do  not  completely  envelop  the  cord ;  f,  fibrous  bundles 
composing  the  cord. 

B.  A  view,  under  the  same  power,  of  two  isolated  endo- 
thelial cell-plates  similar  to  those  which    in  part  cover  the 
fibrous  cord  in  A.    n,  The  nucleus  ;  e,  a  ridge  on  the  surface 
of  the  cell  plate,  which  sinks  into  the  crevice  or  groove 
formed  by  the  apposition  of  two  or  more  bundles. 

C.  A  transverse  view,  under  a  much  lower  power,  of  several 
juxtaposed  fibrous  cords,  such  as  mentioned  above,    f,  The 


fibrous  bundles  cut  across  ;  c,  stellate  bodies,  having  processes 
which  sometimes  communicate  with  those  of  neighboring 
bodies — they  have  been  regarded  as  stellate  corpuscles  or 
cells,  but  are  nothing  more  than  the  cross  cuts  of  the  above- 
mentioned  endothelial  cell-plates.  (All  after  Ranvier.) 

Fig.  3.    Represents,  under  a  moderate  power,   an    elastic 
lamina  of  the  middle  tunic  of  the  Human  aorta.    (Ran- 
vier.) 
b,  Elastic  membrane  ;  a,  elastic  fibres  arising  from  it. 

Fig.  4.  Hyaline  cartilage  of  Man,  .medium  amplification. 

rf,  Structureless  hyaline  matrix,  in  which  are  imbedded 
cells  enveloped  within  a  capsule,  a,  which  latter  is  indicated 
by  the  light  halo;  b,  c,  cells  in  process  of  multiplication. 

Fig.  5.  Section  of  cartilage  from  the  head  of  the  femur  of  a 
Frog,  examined  perfectly  fresh  and  without  any  mount- 
ing fluid.     Very  high  power.     (After  Ranvier.) 
s,  Fundamental  substance,  or  hyaline  matrix  ;  c,  capsule  ; 

n,  double-contoured  nucleus  ;  n',  small  brilliant  nucleolus. 


PLATE    III 


Fig  1. 


. 3. 


Fig. 2. 


c 


FiS  5. 


Fig  4. 


T-  iirclur  *S«n  MK 


CARTILAGE. 


53 


Fig.  24. 


while  the  descendants  have  received  the  name  of 
dauijhler  cells.  If  the  process  of  division  be  slow  each 
new  cell  may  form  around  it 
a  new  capsule  (see  Fig.  24). 
In  this  case  the  mother  cap- 
sule contains  a  series  of 
daughter  capsules.  If,  how- 
ever, the  process  of  multipli- 
cation is  rapid  the  newly 
born  cells  will  not  have  time 
to  secure  the  formation  of  a 
capsule  before  they  give 
birth  to  new  cells.  Hence, 
the  orginal  mother  capsule 
must  now  contain  two  or  a 
greater  number  of  cells  of  a 
more  or  less  embryonal  nature.  The  healthy  carti- 
lage-cell lives,  then,  within  an  envelope  or  shell  which 
it  builds  for  itself  as  a  habitation. 

The  inner  surface  of  this  envelope,  the  cartllaye 
capsule,  forms  the  boundary  of  a  lymph-space,  more  or 
less  spherical,  which  is  normally  quite  filled  by  the  body 
of  the  cartilage-cell  (see  figs.  4,  5,  Plate  III.).  Pre- 
parations of  cartilage  usually  show  the  cartilage-cell 
to  be  more  or  less  angular,  and  occupying  only  a  small 

Fiff.  25. 


PROLIFERATING  CARTILAOE- 
(':;:,!.,-. — c.  Protoplasm  of  the  coll ; 
«,  nucleolus  ;  &,  nucleus  ;  d,  pri- 
mary and  secondary  cartilage  cap- 
sules ;  c,  ground  substance.  In 
one  of  the  card  lag  c-cclls  are  seen 
two  nuclei. 


a.  r 


CARTILAGE  OF  A  CUTTLE-FISH. — a,  d.  Body  of  cell.    &.  Anastomosing  branches 
of  the  cells,     c.  Fundamental  substance.     X  400.     (Kanvie.r.) 

proportion  of  the  space  within  the  capsule.    This  is  a 

distortion,  due  to  the  death  and  shrinking  of  the  cell. 

In  the  depth  of  cartilage  the  capsules  usually  have 

a  tendency  to  assume  the  spheroid  form,  while  to- 


wards the  surface  they  become  more  or  less  flattened 
or  lenticular  in  outline.  In  the  superficial  layer,  at 
the  articular  surfaces,  the  cells  are  quite  flat,  and 
sometimes  branched.  In  the  articular  cartilages,  near 
the  periphery,  where  the  fibrous  tissue  of  the  syno- 
vial  membrane  is  attached,  the  cartilage-cells  are  often 
branched,  and  at  the  line  of  attachment  the  processes 
of  the  branched  cells  sometimes  communicate  with 
those  of  the  connective-tissue  corpuscles  of  the  fibrous 
tissue.  Branched  cells,  like  those  seen,  in  Fig.  25,  are 
not  uncommon  in  hyaline  cartilage  of  some  lower 
animals. 

Matrix. — The  intercellular  substance,  the  ground- 
substance,  or,  as  it  is  technically  called,  the  matrix  of 
hyaline  cartilage,  is  usually  hard,  somewhat  elastic, 
homogeneous,  and  transparent.  In  adult  cartilage, 
after  staining,  the  matrix  faintly  shows,  by  slight  dif- 
erences  in  shade,  very  indistinct  and  shadowy  mark- 
ing for  some  distance  around  the  capsule  (fig.  5,  Plate 
III.).  The  cartilage-cell  seems  to  have  been  a  centre 
around  which  on  all  sides  the  matrix  has  been  de- 
posited in  successive  layers  from  without  inwards,  the 
existing  capsule  being  last  deposited.  Under*  some 
circumstances  the  shadowy  areas  around  the  capsule 
seem  to  be  composed  of  a  number  of  concentric  shells. 
The  whole  ground-substance  appears  to  consist  of  an 
aggregation  of  these  shadowy  areas  surrounding  the 
cells. 

fibrillation  of  matrix. — Sometimes  in  adult  hyaline 
cartilage  the  matrix  is  seen  to  be  very  finely  fibril- 
lated.  This  condition  is  met  with  most  frequently  in 
the  costal  cartilages  of  the  aged,  and  in  the  calcifying 
layer  of  ossification  of  cartilage  (see  fig.  1,  Plate  IV.). 

Embryonal  cartilage. — The  cells  of  hyaline  carti- 
lages may  be  closely  aggregated,  or  they  may  be 
sparsely  distributed  through  the  matrix.  When  the 
intercellular  substance  is  so  small  in  amount  that  it 
is  scarcely  appreciable,  the  cartilage  is  known  as 
parenchymatous  or  embryonal  cartilage. 

In  the  deep  portion  of  articular  cartilages,  in  the 
neighborhood  of  lines  of  ossification,  the  cartilage  cor- 
puscles assume  an  arrangement  in  parallel  rows  more 
or  less  vertical  to  the  articular  surface. 

Perichondrium. — Each  variety  of  cartilage  is  en- 
veloped in  a  fibrous  membrane,  the  perichondrium, 
which  covers  it  everywhere  except  upon  the  articular 
surfaces  and  in  the  lines  of  ossification. 

Calcification  of  cartilage. — Cartilage  may  be  infil- 
trated with  calcareous  particles.  When  this  is  the  case 
lime  granules,  minute  and  more  or  less  angular,  are 
first  deposited  in  the  ground-substance,  immediately 
around  the  cartilage  capsules.  From  these  points  the 


54 


HISTOLOGY. 


infiltration  may  gradually  spread  until  the  whole 
matrix  may  be  incrusted,  and  the  cells  transformed 
into  calcified  elements.  By  transmitted  light  the 
particles  of  lime  are  dark  and  opaque,  large  collec- 
tions of  them  consequently  appear  more  or  less  black. 
By  reflected  light  they  are  brilliant  and  shining.  This 
deposit  of  lirne  does  not  appear  to  permanently  change 
the  constitution  of  the  cells  or  matrix.  Weak  acids 
readily  dissolve  it,  leaving  both  apparently  in  their 
original  condition. 

YELLOW  ELASTIC  OR  RETICULAR  CARTILAGE. 

This  variety  of  cartilage  is  met  with  in  man,  in 
the  Eustachian  tube,  in  the  epiglottis,  and  a  few  other 
places.  It  differs  from  hyaline  cartilage  only  by  the 
presence  in  the  matrix*  of  fine,  yellow  elastic  fibres 
in  greater  or  lesser  numbers.  These  fibres  are  gen- 
erally collected  together  so  as  to  form  a  trabecular 
network  in  the  matrix.  In  the  meshes  thus  formed 
the  cells  are  found  enveloped  in  capsules,  which  are 
surrounded  by  a  variable  amount  of  hyaline  ground- 
substance  (see  fig.  3,  Plate  IV.). 

Near  the  perichondriurn  the  elastic  fibres  gradually 
disappear. 

WHITE  FIBROUS  CARTILAGE. 

This  form  of  cartilage  appears  to  occupy,  histo- 
logically,  an  intermediate  place  between  white  fibrous 
connective-tissue  and  hyaline  cartilage. 

Its  distribution  in  man  is  somewhat  more  exten- 
sive than  the  yellow  elastic  cartilages.  It  is  chiefly 
found  in  the  intervertebral  disks  and  in  the  bursse 
of  tendons. 

The  intercellular  substance  or  the  matrix  consists 
of  white  fibrous  tissue  arranged  in  parallel  bundles. 
Frequently  the  fibres  are  arranged  in  lamellae,  and 
sometimes,  as  in  the  intervertebral  disks  and  the 


symphysis  pubis,  the  bundles  constituting  the  lamellae 
have  a  concentric  arrangement.  The  cells  of  this 
form  of  cartilage  have  the  same  relation  to  the  bun- 
dles as  the  flat  cells  of  Kanvier  do  to  the  parallel 
bundles  of  tendons  or  aponeuroses.  The  cells  them- 
selves are  not  quite  so  flat  or  so  much  branched  as 
the  endothelial  cell-plates  of  tendons.  They  are  en- 
veloped by  the  characteristic  capsule  of  the  cartilage- 
cell  (fig.  2,  Plate  IV.).  In  some  places  the  capsules 
are  surrounded  by  a  very  small  amount  of  hyaline 
substance.  In  the  transition  of  tendon  into  fibro-car- 
tilage  the  tendon-cells  gradually  thicken  and  become 
invested  with  a  capsule,  the  only  visible  change 
noticeable.  In  the  transition  of  fibre-cartilage  into 
hyaline  cartilage,  as  is  Observed  at  the  edges  of  the 
intervertebral  cartilages  for  example,  the  fibrous 
intercellular  substance  slowly  disappears  and  merges 
in  the  Iryaline  matrix,  while  the  cartilage-cells  gradu- 
ally swell  and  approach  the  spherical  form. 

Lymphatics  of  cartilage. — Cartilage,  like  all  the 
other  connective-tissues,  is  permeated  by  lymph  spaces. 
The  cartilage-capsules  are  perforated  by  almost  num- 
berless minute  canals.  The  openings  of  these  minute 
capillary  tubes  or  pores  communicate  at  one  end  with 
the  interior  of  the  capsule,  which  is  a  lymph-space 
containing  the  cartilage -cell,  and  at  the  other  end  open 
into  large  canaliculi  which  ramify  in  the  cartilage 
matrix,  and  which,  in  their  turn,  communicate  witli 
the  lymphatics  of  the  perichondrium. 

BONE  OR  OSSEOUS  TISSUE. 

Bone  is  the  greatest  in  weight  of  all  the  solid  tis- 
sues of  the  organism,  and  is  the  most  extensive  of  the 
groups  of  the  great  connective  system. 

It  presents  for  study  a  ground-substance,  inclosing 
cellular  elements  and  vessels,  both  lymph  and  capil- 


EXPLANATION  OF  PLATE  IV. 


Fig.  1.  Section  of  calcified  and  fibrillated  hyaline  cartilage, 
from  the  costal  cartilage  of  an  old  Man.     High  power. 
a,  Intercellular  matrix  infiltrated  with  minute  calcareous 
granules,  they  are  found  more  densely  aggregated  at  c,  around 
the  cartilage  capsules ;  b,  fine  fibrillae,  imbedded  in  the  in- 
tercellular hyaline  matrix. 

Fig.  2.  Fibro-cartilage  from  the  intervertebral  disk  of  Man. 

High  power, 
a,  Fibrous  matrix  or  intercellular  substance  ;  c,  b,  cells 


contained  within  a  cartilage  capsule,  and  exhibiting  various 
stages  of  multiplication. 

Fig.  3.  Reticular  or  elastic  cartilage,  from  the  epiglottis  of 
Man,  showing  the  so-called  cartilage  cells  in  various 
phases  of  division  within  their   enveloping   capsules. 
High  power. 
b,  Elastic  fibres  imbedded  in  the  intercellular  matrix. 


PLATE    IV 


"- 


Ny" 


Fi<s.2 


Fi<s.S 


T.  si*eltir  »  s«  UtK. 


BONE    OR   OSSEOUS   TISSUE. 


55 


lary.  The  ground-substance  is  dense  and  compact, 
as  at  the  boundary  of  the  medullary  canal  of  long 
bones,  and  at  the  periphery  of  both  long  and  flat 
bones;  or,  on  the  other  hand,  it  is  porous  or  spongy, 
as  in  the  diploe  of  flat  bones,  in  the  interior  of  epi- 
physes,  and  between  the  outer  and  inner  compact 
layers  of  the  diaphyses  of  long  bones. 

Compact  bone. — -The  ground-substance  of  compact 
bone  is  hard  and  brittle,  owing  to  its  infiltration  with 
salts  of  lime,  which  in  the  fluids  of  the  body  are  ordi- 
narily insoluble.  They  are,  however,  readily  dissolved 
by  the  employment  of  acids.  After  decalcification 
through  this  means,  bone  may  readily  be  cut  into 
thin  sections  and  stained.  Thin  plates  of  the  hard, 
brittle  bone,  may  also  be  obtained  by  grinding.  A 
transverse  section  of  the  compact  substance  of  the 
shaft  of  a  long  bone  prepared  by  the  latter  method, 
and  mounted  dry,  presents  an  appearance,  when  ex- 
amined under  a  high  power  of  the  microscope,  which 
is  very  fairly  represented  by  fig.  1,  Plate  V. 

Haversian  canals. — The  ground-substance  is  per- 
meated by  a  number  of  small  canals,  the  Ilaversian 
canals,  which  have  a  general  direction  mainly  parallel 
with  the  axis  of  the  shaft.  They  intercommunicate 
by  means  of  short  transverse  or  oblique  branches, 
thus  forming  a  network  of  elongated,  and  more  or 
less  rectangular  meshes.  The  Haversian  canals  con- 
vey a  capillary  bloodvessel  and  one  or  more  lymph- 
vessels,  besides  a  variable  amount  of  delicate,  loose 
connective-tissue  of  a  reticular  variety,  inclosing  cel- 
lular elements, — a  tissue  essentially  identical  with  the 
bony  marrow  which  fills  the  Haversian  spaces  of 
spongy  bone. 

Arrangement  of  bony  lamellae. — Between  the  Ha- 
versian canals  of  compact  bone  the  ground-substance 
is  arranged  in  the  following  manner:  Immediately 
around  the  canal  the  bony  fibrous  tissue  shows  from 
four  to  fifteen  or  twenty  concentric  lamellae,  the  number 
varying  according  to  the  age  of  the  formation.  The 
greater  the  age  the  more  numerous  are  the  concentric 
lamella.  The  Haversian  canals,  with  their  surround- 
ing concentric  lamella?,  are  known  as  iheHaversian  sys- 
tems. Between,  and  separating  the  Haversian  systems, 
the  ground-substance  is  constituted  by  what  have  been 
termed  the  interstitial  lamellae.  They  comprise  bands 
of  osseous  substance  of  variable  width,  running  in 
various  directions.  Among  these  interstitial  lamella? 
of  variable  direction  are  some  bands  of  lamella  which 
pursue  a  course  in  general  parallel  to  the  periosteal 
surface  of  the  bone.  These  are  known  as  the  parietal 
lamellae.  Running  among  the  interstitial  and  the 
parietal  lamellae  are  sometimes  found  a  small  number 


of  scattered  elastic  fibres  which  are  very  difficult  to 
demonstrate.  Interlacing  with  the  parietal  and  inter- 
stitial lamella?  are  found  a  few  small  bundles  whose 
basis  is  white  fibrous  tissue,  and  whose  direction  is 
more  or  less  perpendicular  to  that  of  the  lamella? 
which  they  penetrate  (see  fig.  3,  Plate  V.).  They 
are  called  perforating  fibres,  or  fibres  of  Sharpey,  and 
are  supposed  to  be  the  remains  of  bundles  of  white 
fibrous  tissue  originally  forming  a  part  of  the  inner 
layer  of  the  periosteum,  for  at  the  periphery  of  the 
bone  similar  fibres  are  continuous  with  fibrous  bun- 
dles belonging  to  the  inner  layer  of  that  covering. 

In  flat  bones  or  in  thin  bony  plates,  the  compact 
substance  presents  essentially  the  same  features.  The 
arrangement  of  the  Haversian  systems,  however,  is 
by  no  means  so  regular  as  in  the  diaphyses  of  long 
bones. 

Bone  corpuscles. — Between  the  bony  lamellae  of  these 
different  systems  are  numbers  of  fymp/f-spaces,  in  which 
lay  connective-tissue  corpuscles,  just  as  in  other  forms 
of  lamellar  fibrous  tissue.  These  lyrnph-spaces  and 
their  cellular  contents  constitute  the  so-called  bone- 
corpuscles.  Each  lymph-space  is  in  communication 
with  its  neighbors  by  means  of  minute  canaliculi,  the 
branches  of  the  so-called  bone-corpuscle.  These 
canaliculi  penetrate  the  bone  lamella?,  and  pass 
through  them,  usually  nearly  perpendicular  to  the 
direction  of  the  latter.  When  a  thin  preparation 
of  compact  bone  is  made  by  grinding,  and  the  thin 
plate  is  mounted  dry,  these  lymph-spaces  and  their 
canalicular  branches  are  filled  with  air,  and  by  trans- 
mitted light  consequently  appear  dark  upon  a  light 
ground.  In  Haversian  systems  cut  transversely,  the 
body  of  the  bone-corpuscle  is  seen  in  profile,  and 
consequently  presents  an  ovoid  or  fusiform  outline, 
the  long  axis  being  parallel  with  the  course  of  the  la- 
mellae. The  canalicular  branches,  more  or  less  straight, 
and  running  perpendicular  to  the  length  of  the  con- 
centric lamellae,  give  to  the  Haversian  systems  a 
beautiful  striated  aspect,  the  fine  stria?  radiating  from 
the  Haversian  canal  as  a  centre.  In  the  interstitial 
and  parietal  lamella?  the  canaliculi  produce  a  visible 
transverse  striation.  The  canaliculi,  besides  forming 
an  intercommunication  between  the  lymph-spaces  of 
the  ground-substance,  also  bring  them  into  connection 
with  the  lymph-vessels  of  the  Haversian  canals. 

When  a  so-called  bone- corpuscle  with  its  canalicular 
branches  is  isolated  from  the  surrounding  bony  sub- 
stance in  which  it  is  imbedded,  and  is  properly 
treated,  it  is  found  to  consist  of  an  elastic  shell  form- 
ing a  branched  lymph-space.  Within  this  branched 
lymph-space  floats  a  flat  connective-tissue  cell  similar 


66 


HISTOLOGY. 


to  the  flat  branched  cells  of  loose  connective-tissue. 
This  is  really  the  bone-cell.  Its  structure  is  identical 
with  that  of  the  connective-tissue  corpuscle.  It  gives 
off  delicate  branches  which  enter  and  pass  some  dis- 
tance along  the  minute  canaliculi. 

Spongy  bone. — The  spongy  portion  of  lone  offers  a 
gross  formation  quite  different  from  that  which  we 
have  just  studied  in  the  compact  tissue.  In  the  latter, 
the  Haversian  canals  occupy  a  small  area  in  proportion 
to  that  of  the  intervening  ground-substance,  and  con- 
tain a  minimum  of  marrow-tissues.  In  the  spongy 
substance,  on  the  contrary,  the  bony  matter  is  small 
in  amount  compared  to  the  area  of  the  spaces  which 
correspond  to  the  Haversian  canals  of  the  compact 
tissue,  but  which  here  are  called  Haversian  spaces. 
Moreover,  the  Haversian  spaces  are  filled  by  a  cellu- 
lar mass,  known  as  the  bony  marrow,  in  which  nume- 
rous bloodvessels  with  extremely  thin  and  delicate 
walls  ramify.  The  large  Haversian  spaces  are  not 
surrounded  by  concentric  lamellae,  but  are  separated 
from  each  other  by  more  or  less  delicate  trabecula?  of 
bone  which  represent  the  interstitial  and  parietal 
bands  of  the  compact  substance,  and  which  have  a 
minute  structure  identical  with  them.  These  bony 
trabeculae  form  a  loose  spongy  osseous  network  in 
the  meshes  of  which  rests  bone  marrow. 

Marrow  of  bone. — The  marrow  of  bone  is  an  extreme- 
ly vascular,  cellular  tissue  which  presents  two  chief 
varieties,  the  yellow  and  the  red.  The  yellow  marrow 


of  bone  is  especially  found  in  the  central  cavities  of 
the  long  bones.  It  consists  mainly  of  fat- vesicles  such 
as  are  met  with  in  adipose  tissue,  and  it  is  the  fat-cells 
which  give  the  tissue  its  yellowish  color.  Among 
these  adipose  vesicles  are  a  variable  number  of  other 
elements.  A  few  flat,  more  or  less  branched  connec- 
tive-tissue cells  together  with  a  sparse  amount  of  deli- 
cate coniiective-tissue  fibres  sometimes  form  thin  septa 

Fig.  26. 


CELLS  FKOM  THE  MARROW  OF  BONE  DURINQ  THEIU  PERIOD  OF  DEVRLOI»MENT.— a, 
b.  MuUinuclear  "giant  cells"  (Prey).  e,/,g.  Lymph-cells  from  the  marrow  of 
the  tibia  of  the  Guinea-Pig,  examined  in  the  serum  of  the  blood  ;  c,  d,  h,  after 
the  action  of  alcohol  and  water  33  per  cent.  i,}.  So-called  osteoblasts  from  the 
femur  of  a  new-born  Dog,  after  the  action  of  alcohol  33  per  cent.  High  power. 
(Ranvier.) 

between  the  vesicles.     There  are  also  in  the  latter 
location  a  small  number  of  cellular  elements,  which, 


EXPLANATION  OF  PLATE  V. 


Fi 


ig.  1.  Transverse  section  of  compact  substance  of  shaft  of 
a  long  bone  of  Man.  High  power. 

a,  The  circumferential  or  peripheral  lamellae,  whose  course 
is,  in  the  main,  parallel  to  the  surface  of  the  bone  ;  b,  the 
concentric  lamellae  constituting  the  Haversian  systems,  in 
the  centre  of  which  are  the  Haversian  canals,^  g  ;  another 
system  of  lamellae  is  represented  at  c,  d,  the  interstitial  or 
intermediate  lamellae  ;  It,  bone  corpuscles,  with  their  radia- 
ting canaliculi. 

Fig.  2.  Longitudinal  section  of  similar  bony  tissue.     Same 

power. 

a,  Haversian  canals ;  c,  their  walls  ;  d,  bone  corpuscles, 
separated  by  the  bone  lamellae,  whose  direction  is  usually 
parallel  with  that  of  the  Haversian  vessels. 

Fig.  3.  Some  of  the  bony  lamellae  from  an  intermediary  or 
interstitial  system,  forcibly  stripped  off  after  decalcifi- 


cation  of  the  bone,  showing  the  bone  corpuscles,  and 
the  fibres  of  Sharpey,  c. 

Fig.  4.  Vertical  section  of  the  deep  layer  of  ossifying  por- 
tion of  a  metatarsal  bone,  showing  some  of  the  phases 
of  development  of  bone  from  cartilage.  High  power. 
(After  Miiller.) 

a,  Cartilage  cells,  arranged  in  rows,  some  with  shrunken 
cell  bodies ;  6,  ground  substance  of  the  cartilage ;  c,  medul- 
lary canal  in  process  of  formation,  and  containing  vessels 
and  medulla  cells ;  d,  the  remains  of  the  ground  substance 
of  the  cartilage,  covered  by  a  thin  layer  of  newly-formed 
bone,  g;  e,  osteoblasts  covering  the  recently  formed  bone ; 
/,  a  bone  cell  in  process  of  forming  a  bone  corpuscle,  still 
connected  with  the  osteoblastic  layer  of  cells ;  k,  recently 
developed  bone  corpuscle,  containing  a  young  bone  cell ;  m, 
a  medullary  space,  from  which  the  contents  have  been  dis- 
placed. 


PLATE    V 


Fig  1 
a  h 

-    ^:'%    *:%  '..          N 

'^••^S  '»  "--^:'-:>iX 


*&  ™'M 


$f 
?<*, 


^,,' 

rl      ' 


a.  ^ 


T   SijcHrt  i  San  lit]-. 


BONE    OR   OSSEOUS    TISSUE. 


57 


by  their  size  and  structure,  cannot  when  isolated  be 
distinguished  from  colorless  lymph-corpuscles.  The 
(Smallest  of  the  latter  have  been  called  medulla  cells 
(d,f,  Fig.  26).  Multinuclear  giant  cells  (myeloplaxes, 
«,  6,  Fig.  26)  are  also  present  in  small  numbers.  The 
latter  elements  consist  of  a  large,  soft,  membraneless, 
irregularly-formed,  'sometimes  branched  and  flattened 
cell-body,  of  a  fine  granular  appearance,  and  contain 
a  fibrillar  network  like  that  of  other  cells.  They 
inclose  a  large  number  of  nuclei.  The  vessels  are 
similar  to  those  of  the  other  varieties  of  marrow. 

Red  marrow  of  bone  is  met  with  in  the  Haversian 
spaces  of  spongy  bone.  To  the  naked  eye  it  differs 
from  the  yellow  marrow  mainly  by  the  entire  ab- 
sence of  fat  vesicles,  or  by  their  presence  only  in  very 
small  numbers,  and  by  the  extreme  vascularity  of  the 
tissue.  This  form  of  marrow  consists  of  reticulated 
fibres  similar  to  those  of  lymph-glands  or  lymphoid 
tissues  to  be  described  later.  In  the  meshes  of  this 
reticulated  tissue,  cells  of  the  following  forms  are 
closely  crowded :  1st,  perhaps  an  extremely  few  fat- 
cells;  2d,  large  numbers  of  medulla-cells ;  3d,  con- 
siderable numbers  of  multinuclear  giant  cells;  4th, 
polynucleated  cells,  which  have  a  diameter  slightly 
larger  than  that  of  the  red  blood-corpuscles,  and 
which  possess  a  smooth,  apparently  homogeneous 
body  presenting  a  yellowish-green  tinge,  —  these 
cells,  according  to  Neumann  and  Bizzozero,  subse- 
quently become  converted  into  red  blood-corpuscles, 
by  losing  their  nucleus  and  becoming  bi-concave ; 
5th,  along  the  osseous  trabeculas  are  a  single  row  of 
cells,  which  are  larger  than  the  ordinary  colorless 
elements  of  the  marrow,  and  are  more  or  less  pris- 
matic or  flattened  by  mutual  pressure.  They  have 
been  called  by  Gegenbauer  osteoblasts,  since  they  seem 
to  take  an  active  part  in  the  formation  of  the  bony 
substance. 

All  of  the  foregoing  cellular  elements  possess,  in  a 
more  or  less  active  degree,  the  power  of  movement. 

Besides  the  cellular  forms  already  described  there 
are  always  present  in  the  bony  marrow  some  colored 
cells,  which  are  not  distinguishable  from  red  blood- 
corpuscles. 

Red  bone-marrow  is  very  richly  supplied  with 
bloodvessels,  which  have  extremely  thin  and  delicate 
walls. 

Periosteum. — The  external  surface  of  bone  is  covered 
by  a  fibrous  membrane — the  periosteum.  It  consists  of 
two  layers,  an  outer  and  an  inner.  The  outer  layer  is 
composed  of  one  or  more  lamellaa  of  dense  white  fibrous 
tissue,  the  direction  of  whose  bundles  is  parallel  to 
the  surface  of  the  bone.  Among  these  white  fibrous 
8 


bundles  is  a  limited  quantity  of  fine  yellow  elastic 
fibres,  and  in  the  lymph-spaces  formed  by  the  apposi- 
tion of  the  bundles  are  cellular  elements  similar  to 
those  of  dense,  white  fibrous  tissue.  In  this  external, 
or  fibrous  layer  of  the  periosteum,  blood  and  lymph- 
vessels  ramify  and  form  networks. 

The  inner  or  osteogenetic  layer  of  the  periosteum 
consists  of  an  extremely  loose  fibrous  tissue,  the 
meshes  of  which  are  filled  by  cells  very  similar  to  the 
osteoblasts  described  as  existing  upon  the  trabeculse 
of  spongy  bone.  Among  these  are  numbers  of  ele- 
ments which  present  characters  similar  to  those  of 
lymph-corpuscles.  The  osteogenetic  layer  of  the  peri- 
osteum is  richly  supplied  by  bloodvessels,  which  run 
among  the  cells  occupying  the  meshes. 

Beneath  the  periosteum  the  surface  of  growing 
bone  is  covered  by  a  bony  network,  the  meshes  of 
which  are  crowded  by  cells  which  are  contiguous 
with  those  which  fill  the  inter-fibrillar  spaces  of  the 
osteogenetic  layer.  Here  and  there  the  most  super- 
ficial portion  of  this  bony  network  sends  a  pointed 
and  somewhat  curved  spicule  of  bone  into  the  depth 
of  the  osteogenetic  layer  of  the  periosteum.  The 
points  of  these  somewhat  conical  spicules  are  usually 
continuous  with  fibrous  bundles  of  the  osteogenetic 
layer.  The  surface  of  the  trabecula3  forming  this 
osseous  network,  as  well  as  of  the  bony  spicules  which 
project  into  the  osteogenetic  layer  of  the  periosteum, 
are  covered  by  the  so-called  osteoblasts  of  Gegenbauer, 
through  the  agency  of  which  not  only  the  bony  tra- 
beculse  and  spicules  springing  therefrom  increase  in 
size,  but  also  the  fibrous  bundles  at  the  end  of  the 
spicules  are  converted  into  bone.  In  this  manner  the 
bone  grows  beneath  the  periosteum. 

OSSIFICATION. 

Bones  increase  in  length  by  a  process  which  is 
known  as  ossification.  In  young  growing  bone,  the 
epiphyses  are  united  to  the  diaphyses  by  the  inter- 
vention of  a  plate  of  cartilage — the  intermediary 
cartilage.  The  successive  conversion  into  spongy 
bone  of  the  layers  of  this  cartilage  which  are  in 
immediate  apposition  with  the  diaphysis,  furnishes 
an  excellent  opportunity  to  examine  the  process  of 
ossification  of  cartilage. 

Line  of  ossification. — A  longitudinal  section  passing 
through  the  diaphysis  and  intermediary  cartilage  of  a 
long  bone  shows  to  the  naked  eye  a  straight  line  of 
union  between  the  spongy  bone  and  the  cartilage. 
This  line  is  called  the  line  of  ossification.  The  carti- 
lage above  it  seems  to  be  divided  more  or  less  dis- 


58 


HISTOLOGY. 


tinctly  into  three  layers — the  lowest  layer  or  the  one 
forming  the  line  of  ossification  is  more  or  less  opaque, 
the  middle  layer  is  unusually  transparent,  the  upper 
layer  is  quite  normal  in  appearance.  If  a  thin  piece 
of  the  spongy  bone  and  cartilage  is  shaved  off',  and 
after  being  properly  prepared  for  examination,  is 
placed  under  the  microscope,  the  following  appear- 
ances may  be  noted  (see  fig.  4,  Plate  V.).  In  the 
upper  layer  or  zone  of  cartilage,  the  capsules  and  in- 
tercellular ground-substance  are  normal.  In  the 
middle  layer,  the  cells  have  begun  to  enlarge  and  to 
multiply.  Some  of  them  show  signs  of  disintegration, 
and  the  spaces  which  contain  the  cells  have  also  con- 
siderably increased  in  dimensions.  The  increase  is 
mainly  in  a  direction  perpendicular  to  the  line  of 
ossification,  and  on  account  of  this  tendency  the  cells 
are  applied  against  each  other  so  as  to  form  linear 
rows.  The  intercellular  substance  is  consequently 
encroached  upon  and  somewhat  softened. 

In  the  lower  zone,  the  cartilage  matrix  which  re- 
mains between  the  now  greatly  elongated  capsules,  in 
consequence  of  the  further  enlargement  of  the  latter, 
is  reduced  to  narrow  trabeculce  which,  are  infiltrated 
with  calcareous  deposits.  The  enlarged  elongated 
capsules  frequently  fuse  together.  They  are  now  in 
part  filled  by  an  embryonal  marrow.  The  cartilage- 
cells  which  occupy  their  upper  ends  approach  a  wedge- 
shape,  and  are  piled  upon  one  another  in  such  a 
manner  that  the  bases  alternate  with  the  spaces  as 
seen  at  a,  fig.  4,  Plate  V. 

In  a  yet  lower  zone,  the  linear  spaces  between  the 
narrow  trabeculae  of  cartilage  matrix  are  completely 
filled  with  a  mass  of  cells  similar  in  every  respect  to 
that  of  the  bony  marrow  in  the  Haversian  spaces,  and 
they  are  now  permeated  by  loops  of  capillary  blood- 
vessels, which  are  in  communication  with  the  vessels 
of  the  marrow  of  the  spongy  bone  below.  The  thin 
trabeeulae  of  cartilaginous  matrix,  separating  these 
spaces,  are  still  infiltrated  with  calcareous  salts.  They 
are  now  more  or  less  completely  encrusted  with  a  thin 
layer  of  osseous  substance  of  variable  thickness  (see 
g,  fig.  4,  Plate  V.). 

This  thin  osseous  incrustation  is  itself  covered  by 
a  layer  of  osteoblasts  of  a  prismatic,  ovoid,  or  some- 
times slightly-branched  outline.  Here  and  there  in 
the  thickest  points  of  this  incrusting  layer  of  osseous 
substance  an  oval-shaped,  incompletely-branched  bone- 
corpuscle  is  visible.  By  carefully  searching  along  these 
incrustations  pouch-shaped  notches  are  occasionally 
met  with  opening  upon  the  surface.  These  are  filled  by 
osteoblastic  cells  which  may  be  connected  with  other 
cells  in  the  osteoblastic  layer  by  broad  or  narrow" 


branches  (see/,  fig.  4,  Plate  V.).  It  is  thus  seen  that 
the  bone-cells  are  osteoblasts  which  have  become  in- 
cluded and  completely  imbedded  in  'the  osseous  sub- 
stance which  they  have  formed  around  them. 

In  a  still  lower  zone,  we  recognize  the  same  general 
features  presented  by  that  last  described.  But  the 
lamellae  of  bone  incrusting  the  cartilaginous  trabeculse 
are  much  thicker,  and  the  cartilage  matrix  has  entirely 
disappeared  in  many  places. 

Below  this  zone,  there  is  no  trace  of  cartilage  matrix, 
and  we  have  only  the  ordinary  structure  of  spongy 
bone.  The  spongy  substance  thus  gradually  en- 
croaches upon  the  intermediary  cartilages  until  they 
finally  disappear.  The  line  of  ossification  presents 
essentially  the  same  features  whether  the  cartilages  be 
intermediary  plates  between  diaphyses  and  epiphyses, 
or  cartilages  which  cover  articular  surfaces. 

It  is  then  noticeable,  that  in  the  growth  of  spongy 
bone  at  the  expense  of  hyaline  cartilage,  the  latter 
does  not  really  become  bone,  is  not  really  ossified, 
but  is  gradually  substituted  and  replaced  by  bony 
substance  which  is  the  direct  product  of  some  of 
the  cells  belonging  to  the  marrow  contained  in  the 
Haversian  spaces  of  the  spongy  bone.  This  latter 
tissue  is  more  or  less  directly  an  outgrowth  from  the 
osteogenetic  layer  of  the  periosteum. 

It  may  be  stated  in  general  terms  that  there  is  no 
ossification  which  does  not  come  either  directly  or 
indirectly  from  the  periosteum  or  from  similar  mem- 
branes which  represent  it.  The  perichondrium  which 
envelops  cartilage  as  the  periosteum  does  the  bone, 
may  be  regarded  as  such  a  representative,  for  the 
structure  of  the  one  is  similar  to  that  of  the  other, 
and  their  functions  are  parallel. 


DEVELOPMENT  OF  BONE. 

The  original  development  of  bone  almost  always  is 
accomplished  through  the  intermediation  of  cartilage. 
The  bones  of  the  face,  however,  and  some  of  those 
of  the  cranium,  are  built  directly  upon  fibrous  mem- 
branes as  a  foundation.  But  whether  or  not  cartilage 
be  employed  in  the  process  of  development,  the  for- 
mation of  bone  always  starts  from  the  periosteum. 

In  the  embryonal  cartilage  which  nearly  always 
precedes  the  formation  of  bone,  we  have  areas  where- 
in certain  changes  take  place  preliminary  to  the  de- 
velopment of  bone.  These  areas  have  been  called 
points  of  ossification.  When  these  points  of  ossifica- 
tion appear  in  cartilage  we  have  a  development  of 
what  has  been  termed  cndochondral  bone. 


DEVELOPMENT    OF    BONE. 


59 


ENDOCHONDRAL  BONE. 

In  an  embryonal  cartilage  which  is  preparing  to  be 
replaced  by  bone,  the  following  succession  of  altera- 
tions may  be  observed. 

Formation  of  embryonal  spongy  bone. — At  a  certain 
point  in  the  inner  or  chondrogenetic  (osteogenetic) 
layer  of  the  perichondrium,  a  loop  or  two  of  capillary 
bloodvessels  project  into  the  cartilage-substance.  In 
advance  of  these  loops  the  cartilage-cells  are  enlarg- 
ing and  multiplying  within  their  capsules,  which 
also  are  enlarged.  These  cells  finally  absorb  the  car 
tilage-matrix  between  them  and  the  mass  of  cellular 
elements  which  surrounds  the  projecting  capillary 
loops;  they  then  communicate  with  the  cells  of  the 
osteogenetic  layer.  By  a  continuation  of  this  pro- 
cess of  absorption  of  the  cartilage  in  front  of  the 
advancing  capillary  loops,  and  by  the  addition  of  the 
contents  of  the  capsules  to  the  mass  of  cells  surround- 
ing the  vessels,  the  embryonal  cartilage  becomes 
channelled  by  vascularizcd  cellular  trabecula?  or 
granulations  springing  from  the  inner  layer  of  the 
perichondrium. 

The  next  step  everywhere  in  the  close  vicinity  of 
the  vascular  granulations,  is  the  enlargement  of  the 
cartilage-capsules,  and  the  multiplication  of  their  cell- 
contents.  This  enlargement  continues,  and  results  in 
the  intercommunication  of  many  adjacent  capsules 
and  the  connection  of  their  contents  with  the  vascu- 
lar granulations.  By  the  enlargement  of  the  spaces 
containing  the  cartilage -cells,  the  intervening  ground- 
substance  is  eaten  away  until  nothing  is  left  of  it  but 
an  irregular  network  of  anastomozing  trabeculas,  the 
surfaces  of  which  are  notched  at  the  place  where  the 
capsules  have  communicated  with  the  general  cellu- 
lar mass.  At  the  same  time  the  cartilage-matrix  in 
this  riddled  area  is  infiltrated  with  a  deposit  of  the 
insoluble  salts  of  lime.  We  have  now  an  area  more 
or  less  irregular  of  calcified,  spongy  cartilage,  the 
meshes  of  this  spongy  formation  being  filled  with,  a 
vascularized  marrow,  similar  in  constitution  to  that 
already  described  when  discussing  the  encroachment 
of  spongy  bone  upon  the  intermediary  cartilage. 

The  next  step  is  the  incrustation  of  the  calcified 
cartilage-trabeculas  with  a  thin  envelope  of  osseous 
tissue.  This  first  takes  place  near  the  central  portion 
of  the  spongy  area,  and  the  bone  is  formed  through 
the  agency  of  osteoblasts  which  cover  the  trabecula. 
This  process  advances  until  the  whole  cartilage  is 
converted  into  spongy  bone.  (Fig.  27). 

Formation  of  bony  marrow. — Sooner  or  later,  in  the 
central  portions  of  this  embryonal  spongy  bone,  the 


osseous  trabeoulte  soften  and  disappear  (osteoporosis). 
In  this  manner  a  central  marrow  cavity  results.  The 
spongy  bone  continues  to  be  slowly  absorbed,  and 
converted  into  marrow  until  finally  the  whole  of  the 
embryonal  spongy  bone  may  be  thus  absorbed. 

Fig.  27. 


TRANSVERSE  SECTION  FROM  THE  FEMUR  OF  A  HUMAN  EMBRYO  ABOUT  ELEVEN 
WEEKS  OLD. — a.  A  medullary  sinus  cut  transversely,  b.  Another,  cut  longitu- 
dinally, c.  Osteoblasts.  d.  Newly  formed  osseous  substance  of  a  lighter  color. 
e.  That  of  greater  age,  /.  Lacunse,  or  blood-corpuscles, with  their  cells,  g.  A 
cell  etill  united  to  an  osteoblast.  (After  Gegenbanr.) 

At  the  same  time  that  the  embryonal  spongy  bone 
is  being  absorbed  at  the  centre,  there  is  a  continual 
new  formation  of  spongy  bone  by  the  osteogenetic 
layer  of  the  perichondrium  (which  latter  may  now  be 
regarded  as  a  periosteum),  practically  identical  with 
that  already  described  for  the  periosteal  growth  of 
bone. 

In  the  older  portions  of  periosteal  spongy  bone,  Ha- 
versian  systems  and  canals  begin  to  form  through  the 
successive  development  of  concentric  lamella  within 
the  Haversian  spaces,  by  means  of  the  osteoblasts 
which  cover  their  surfaces.  Layer  within  layer  is 
thus  formed  in  concentric  deposits  until  the  Haver- 
sian space  is  converted  into  a  Haversian  system  with 
its  narrow  central  canal.  The  original  osseous  tra- 
beculas, which  formed  the  meshes  of  the  periosteal 
spongy  bone,  persist  as  interstitial  bands  between  the 
Haversian  systems. 

Absorption  of  bone  (Osteoporosis'). — Around  the  cen- 
tral marrow-cavity,  which  has  been  formed  asindicated 
above,  a  process  of  absorption  is  at  work.  The  com- 
pact tissue  is  disappearing,  and  being  reconverted  into 
spongy  tissue  through  the  absorption  of  the  Haversian 
systems  and  their  substitution  by  bone-marrow.  The 


00 


HISTOLOGY. 


process  of  absorption  does  not  stop  at  the  accomplish- 
ment of  this  result.  The  interstitial  osseous  trabeculse 
of  the  spongy  bone  next  succumb,  and  the  softened 
area  is  added  to  the  central  cavity. 

Thus  it  is  that  while  the  bones  are  growing  at  the 
periphery  they  are  being  eroded  at  the  centre. 

According  to  Kolliker,  Eindfleisch,  Klein,  and 
others,  solution  of  bone  is  effected  by  the  agency  of 
the  multinuclear  giant-cells.  These  cells  have  con- 
sequently received  the  name  of  osteoclasts.  They  are 
believed  to  elaborate  an  acid  by  whose  action  the 
bony  substance  with  which  they  are  in  contact  is  first 
softened  and  then  dissolved. 

In  the  development  of  bone,  the  various  stages  in 
the  process  of  ossification  may  succeed  each  other 
with  varying  rapidity  in  different  bones,  and  in  dif- 
ferent parts  of  the  same  bone.  In  long  bones,  for 
example,  the  middle  portion  of  the  diaphyses  often 
entirely  consists  of  periosteal  bone,  while  at  the  ex- 
tremities the  embryonal  spongy  bone  has  scarcely 
begun  to  disappear. 

INTERMEMBRANOUS   BONE. 

The  intermembranous  formation  of  bone  is  analo- 
gous to  the  development  of  bone  from  the  periosteum. 
For  instance,  the  bones  of  the  cranium  have  their 
origin  in  a  fibrous  membrane  which  soon  presents  a 
division_into  two  layers  similar  both  in  structure  and 
function  to  the  outer  and  inner  layers  of  the  perios- 

Fig.  28. 


OsTEOBT.ASTB    FROM    THE    PAHIETAL    BONE    OF    A    TlfMAN    EMBRYO   THIRTEEN 

WEEKS  OLD. — a.  Bony  septa,  with  the  cells  of  the  lacuna,  or  bone-corpuscles. 
6.  Layers  of  osteoblasts.  c.  The  latter  in  transition  to  bone-corpuscles.  Very 
high  power.  (Gegenbaur.) 


teum.  Spongy  bone  is  formed  by  the  inner  or  osteo- 
genetic  layer  precisely  in  the  same  manner  as  it  is 
formed  beneath  the  periosteum  of  other  bones.  This 
spongy  bone  is  converted  into  compact  substance  by  the 
same  method,  and  finally  osteoporosis  progresses  in  a 
manner  already  familiar. 


TEETH. 

Although  the  first  rudiments  of  the  teeth  are  off- 
shoots from  the  epithelium  covering  the  surface  of 
the  gums,  and  although  the  enamel  which  covers  the 
exposed  surface  of  the  fully-developed  tooth  is  of  epi- 
thelial derivation,  yet  the  greater  portions  of  the  teeth, 
namely,  the  dentine,  the  cement,  and  the  pulp,  are  of 
connective-tissue  origin,  and  may  properly  be  classed 
with  the  connective-tissues.  Because  of  the  entrance 
of  bone  into  their  structure,  as  well  as  for  other  rea- 
sons, an  examination  of  their  histology  would  seem 
to  have  an  appropriate  place  after  the  study  of  bone. 

Development  of  the  teeth. — The  first  rudiment  of  the 
tooth  is  met  with  early  in  embryonic  life,  at  a  period 
when  the  connective-tissue  of  the  gum  has  scarcely 
advanced  in  development  beyond  the  state  of  fibrous 
mucous-tissue.  It  is  observed  in  the  form  of  a  club- 
shaped  duplicature  of  the  stratified  epithelium  of  the 
gum.  (See  Fig.  29.)  This  epithelial  infolding  is  con- 
Fig.  29. 


VERTICAL  SECTION  OF  THE  UPPER  JAW  OK  A  POSTAL  SHEEP,  about  1%  inches 
long,  showing  the  enamel-germ,  with  the  semilunar  rudiments  of  the  dentine- 
germ  and  dental  sac  in  transverse  section.  1.  Dental  groove ;  2.  Palatal  pro- 
cess. Magnified  50  diameters. 

stituted  externally  by  a  single  layer  of  columnar  epi- 
thelia,  identical  with  those  which  form  the  deepest 
layer  of  the  covering  of  the  gum,  and  internally  by 
a  collection  of  polyhedral  epithelial-cells.  These 
cells,  like  those  of  various  other  epithelial  coverings, 
are  held  together  by  an  intercellular -cement-sub- 
stance. 

This  club-shaped  mass  of  epithelial  cells  is  the  pri- 
mary enamel- or (jan.  Later  this  club-shaped  mass  pene- 
trates deeper  into  the  connective-tissue  and  increases 
greatly  in  thickness,  at  the  same  time  changing  its 
outline.  The  club-shaped  extremity  has  now  spread 
out  and  become  indented  by  a  slight  elevation  of  the 
connective-tissue  which  has  begun  to  advance  into  it. 
(See  /,  Fig.  30.)  This  elevation  is  the  first  appearance 
of  what  will  subsequently  constitute  the  dentine  and 
the  pulp  of  the  tooth.  The  milk,  or  first  teeth,  are  now 


TEETH. 


61 


00< 

in  full  process  of  development.  A  preparation  for  the 
growth  of  the  permanent  teeth  is,  even  at  this  stage, 
often  to  be  met  with  in  the  shape  of  an  offshoot  from 


Fig.  30. 


I ce 


SAME, ATA  LATER  PERIODOF  DEVBLUPMENT. — a.  Epithelium.  6.  Younger  layer 
of  epithelium,  c.  luferior  layer  of  the  epithelium,  e.  Enamel-organ.  /.  I)en- 
tiue-gcrm  or  papilla,  g,  h.  Inner  and  outer  layers  of  the  sacculua  that  is  about 
to  form.  (Carpenter.) 

the  epithelial  mass  already  spoken  of  as  the  primary 
enamel-organ.    4,  Fig.  31,  represents  such  an  epithelial 

Fig.  31. 


VERTICAL  SECTION  OF  THE  LOWER  JAW  OF  A  HUMAN  FOETUS,  measuring  about 
four  inches  in  length,  magnified  25  diam.  1.  Dental-groove.  2.  Remains  of  the 
enamel-germ.  3.  Enamel-organ  of  a  deciduous  tooth,  presenting  epithelium  on 
both  its  outer  and  inner  surface,  i.  e.t  where  it  lines  the  saccnlus  and  where  it 
covers  the  papilla.  4.  Enamel-germ  of  the  permanent  tooth.  5.  Dentine-germ. 
6.  Section  of  inferior  maxilla.  7.  Meckel's  cartilage.  The  dental  sacculus  will 
boobserved  to  present  a  number  of  fine  papilla;  opposite  the  dental  papiliie. 
(Carpenter.) 

offshoot  after  the  changes  in  the  growth  of  the  milk- 
tooth  have  so  far  progressed  that  the  connection  with 
the  enamel-organ  of  the  latter  has  been  severed. 

Fig.  31  represents  a  much  later  stage  in  the  forma- 
tion of  the  tooth.  The  connective-tissue  papilla  has 
grown  into  the  enamel-organ  until  the  latter  has  been 
completely  invaginated.  The  enamel-organ  now 
covers  the  apex  and  sides  of  the  tooth -papilla  like  a 
cap,  and  it  has  been  cut  off  from  its  former  connec- 
tion with  the  epithelial  covering  of  the  gum.  This 
cap-shaped  epithelial  mass  is  termed  the  secondary 
enamel-organ.  Through  the  invagination  of  the  epi- 


thelial mass  constituting  the  enamel-organ,  it  results 
that  the  cap  covering  the  papilla,  when  seen  in  section 
longitudinal  to  the  long  axis  of  the  tooth,  seems  to 
be  formed  by  three  principal  layers.  The  uppermost 
is  composed  of  a  single  row  of  cubical  epithelium ;  the 
lowest  layer  consists  of  a  single  row  of  long  cylindri- 
cal cells;  the  middle  layer  is  formed  of  more  or  less 
compressed  and  branched  epithelial  cells,  with  a  large 
amount  of  intercellular  cement  between  them.  They 
contain  small  oval  or  spherical  nuclei,  and,  according 
to  some  authors,  afford  with  the  intercellular  substance 
an  example  of  mucous-tissue.  Klein  denies  to  this 
layer  any  other  than  an  epithelial  constitution. 

It  is  the  lowest  layer  of  long  columnar  or  pris- 
matic epithelial  cells  which  ultimately  furnishes  the 
enamel  of  the  tooth.  The  two  upper  layers  gradu- 
ally diminish  in  thickness,  and  finally  form  a  thin 
epithelial  covering,  which  is  found  upon  the  surface 
of  the  enamel  when  the  tooth  first  makes  its  appear- 
ance above  the  gurn  (membrane  of  Nasmytli). 

At  first  the  lower  layer  of  enamel-cells  is  separated 
from  the  papilla  by  a  thin  elastic  membrane,  the  re- 
mains of  the  basement-membrane  upon  which  the 
epithelium  of  mucous  surfaces  is  implanted.  Later 
this  disappears,  when  the  enamel  rests  directly  upon 
the  dentine,  which,  as  we  shall  see  below,  is  formed 
bv  the  papilla.  It  is  still  a  mooted  question  whether 
the  enamel  of  the  tooth  is  secreted  by  the  lower  layer 
of  columnar  cells,  or  whether  it  is  the  product  of  a 
direct  transformation  of  the  cells  themselves. 

The  dentine  of  the  tooth  is  formed  by  the  media- 
tion of  a  double  row  of  branched  fusiform  and  colum- 
nar cells,  which  cover  the  pulp  or  papilla. 

The  dental  cement,  or  bony  incrustation  of  the  den- 
tine in  the  root  and  neck  of  the  tooth,  is  developed 
from  the  fibrous  tissue  of  the  dental  processes  or 
alveoli.  This  tissue  here  has  the  structure  and  func- 
tions of  the  periosteum  of  bone. 

STRUCTURE  OF  THE  TEETH. 

The  fully-developed  tooth  consists  of  a  crown,  neck, 
and  one  or  more  roots,  which  like  the  long  bones 
have  a  central  marrow  cavity.  In  this  central  cavity 
run  the  nerves  and  walls  of  the  vessels. 

Dentine. — Nearly  the  whole  solid  portion  of  the 
tooth  is  formed  of  a  hard,  compact,  brittle  substance 
called  dentine.  In  the  crown,  the  dentine  is  covered 
by  a  coating  of  enamel,  the  hardest  substance  met  with 
in  the  human  frame.  In  the  neck  and  roots  the  den- 
tine is  incrusted  by  a  shell  of  true  bone  of  varying 
thickness.  This  incrustation  of  bone,  technically 


62 


HISTOLOGY. 


termed  cement,  is  thickest  at  the  deep  end  of  the 
root.  It  gradually  thins  off  toward  the  neck,  until 
at  this  location  it  is  lost^in  the  enamel. 

Dentinal pulp. — The  dentinal  pulp  consists  of  an  in- 
tricate reticulum  of  delicate  branched  connective-tis- 
sue corpuscles,  with  proportionally  large  and  distinct 
round  or  oval  double- contoured  nucleus,  and  a  small 
amount  of  cell-body,  except  that  which  constitutes 
the  branched  processes.  Among  these  processes  is  a 
small  number  of  lymphoid  corpuscles  and  delicate 
connective-tissue  fibres.  The  capillary  bloodvessels 
have  an  investing  cellular  sheath  just  as  in  the  fibrous 
form  of  mucous-tissue.  Upon  the  external  surface 
of  the  pulp  is  placed  a  double  layer  of  branched 
columnar  and  fusiform  cells,  already  alluded  to.  The 
cells  nearest  the  pulp  are  more  or  less  fusiform  or 
stellate,  with  processes  running  into  the  pulp,  and  a 
few  short  lateral  branches  also,  which  connect  one 
cell  of  the  row  with  another.  The  outer  ends  of  the 
cells  of  this  row  taper  off  into  a  fine  long  extremity, 
which  passes  between  the  cells  of  the  outer  row,  and 
perhaps  beyond  them  into  the  deutinal  canals. 

Odontoblasts,  and  dentinal  fibres. — The  outer  row  of 
columnar  cells  (so-called  odontoblasts)  is  in  contact  with 
the  dentine.  These  cells  are  more  or  less  club-shaped, 
with  the  thick  end  of  the  club  toward  the  pulp.  The 
nucleus,which  is  usually  somewhat  oval  in  shape,  is  in 
this  portion  of  the  cell.  The  outer  end  of  the  club- 
shaped  cell  tapers  off  into  a  fine,  long,  somewhat  tough, 
and  apparently  elastic  process  (dentinal  fibre  of  Tomes). 
This  long  process  of  the  odontoblast  passes  outward 
through  the  dentine,  and*  in  doing  so  frequently 
branches.  The  general  course  of  the  main  fibres  is 
straight  or  slightly  wavy,  and  is  perpendicular  to  the 
external  surface  of  the  dentine.  By  means  of  the 
lateral  branches  anastomoses  are  frequently  formed 
with  the  processes  of  neighboring  odontoblasts.  Ac- 
cording to  most  recent  investigators,  the  dentinal 
fibre  is  surrounded  by  a  thin  structureless  membrane, 
the  dentinal  sheath  of  Neumann.  The  interstitial 
substance  between  these  dentinal  sheaths,  which  latter 
constitute  the  dentinal  canals,  is  a  dense  reticular 
substance  made  extremely  hard  and  brittle  by  infil- 
tration with  the  carbonates  and  phosphates  of  lime. 
When  a  thin  plate  of  dentine  is  mounted  dry  the 
dentinal  canals  arc  filled  with  air,  and  when  examined 
by  transmitted  light  appear  dark,  like  the  canaliculi 
of  bone-corpuscles  similarly  prepared.  According  to 
Klein,  the  dentinal  fibres  which  lie  in  the  dentinal 
canals  are  the  processes  of  the  inner  row  of  the  double 
layer  of  cells  covering  the  pulp,  and  have  no  distinct 
connection  with  the  outer  row  of  odontoblasts.  The 


same  author  thinks  that  those  processes  of  the  latter 
which  enter  the  dentine,  become  calcified  to  form  the 
interstitial  substance  between  the  dentinal  canals. 
Nerve-fibres  have  been  traced  between  the  odonto- 
blasts. 

Inter  globular  spaces. — At  the  outer  surface  of  the 
dentine  the  dentinal  canals  open  into  what  are  known 
as  the  interglobular  spaces  (b,  Fig.  32). 

These  spaces  are  bounded  on  the  side  of  the 
dentine  by  more  or  less  globular  projections  of 
the  ground-substance.  They  contain  branched  cor- 
puscles, apparently  similar  in  every  respect  to 


Fig.  32. 


SECTION  THROUGH  THE  ROOT  OF  A  MOLAR  TOOTH. — a.  Dentine  traversed  by  its 
tubuli.     ft.   Nodular  layer,     n.  Cementum.     (Carpenter.) 

branched  bone-cells.  Their  branches  are  continuous 
with  the  dentinal  fibres,  and  with  branches  of  cells  in 
neighboring  interglobular  spaces.  Where  the  dentine 
is  covered  with  cement,  these  spaces  communicate 
with  adjacent  bone-corpuscles,  by  means  of  the  fine 
canaliculi  of  the  latter.  Beneath  the  enamel  the  inter- 
globular spaces  send  a  few  short  and  irregular  blind 
tubes  among  the  deep  ends  of  the  enamel  prisms. 

Cement  (cementum). —  The  cement,  or  bony  crust 
around  the  root  of  the  tooth,  presents  the  laminated 
ground-substance  and  the  branching  corpuscles  of 
bone.  Sharpey's  fibres  arc  present  in  small  num- 
bers. In  the  thickest  portions,  even  Haversian  sys- 
tems with  their  small  central  canals  are  sometimes 
met  with.  Except  in  these  rare  instances  of  Haver- 
sian systems,  the  lamellae  are  mainly  found  parallel 
to  the  surface  of  the  root.  The  bone-corpuscles  are 
sometimes  unusually  large ;  they  possess  numerous 
branched  canaliculi,  having  the  ordinary  relations  and 
structure  of  bone-corpuscles  elsewhere,  and  they  in- 
close typical  bone-cells. 

Enamel.  —  The  enamel  of  the  fully  formed  and 
healthy  tooth  is  densely  calcified.  Seen  under  'a 
high  power,  in  a  thin  section  vertical  to  the  sur- 
face, the  enamel  appears  to  be  formed  of  closely- 


MUSCLE. 


63 


packed  strias,  whose  direction  in  general  radiates 
from  the  pulp-cavity  as  a  centre.  In  certain  spots 
these  radiating  striae  are  crossed  by  less  distinct  lines 
running  mainly  parallel  to  the  surface  of  the  enamel 
(transverse  striae).  Besides  these  fine  striations,  there 
are  often  two,  three,  or  more  narrow,  faint,  darkish 
stripes  (parallel  stripes  of  Re.tzius)  of  considerable 
length ;  they  exhibit  a  slightly  undulating  course,  and, 
as  a  rule,  run  parallel  to  the  enamel-surface. 

The  significance  of  these  stripes  is  not  fully  under- 
stood. They  may,  perhaps,  represent  the  division  be- 
tween successive  deposits  of  enamel.  The  places  at 
which  transverse  strise  are  seen  crossing  the  radiating 
stria3,  contain  enamel-fibres  running  in  opposite  direc- 
tions. A  minute  description  of  the  radiating  stride 
will  suffice  for  both.  They  consist  of  long  prisms  or 
cylinders  of  calcified  enamel-cells.  When  seen  in 
transverse  section  these  enamel-prisms  appear  more 
or  less  regularly  hexagonal  in  outline  (A,  Fig.  33).  In 
longitudinal  section  after  maceration  in  hydrochloric 
acid,  the  enamel-prisms  present  the  appearance  rep- 
resented in  B,  Fig,  33.  At  regular  intervals  the 
transparent  hyaline-substance  of  the  prism  is  seen  to 
be  crossed  by  extremely  minute  lines.  A  further 
maceration  in  the  acid  results  in  the  breaking  up  of 

Fig.  33. 


DIAGRAMMATIC  REPRESENTATION  OF  THE  STRUCTURE  OF  ENAMEL. — A.  Trans- 
Verse  section  of  enamel,  showing  the  hexagonal  form  of  its  prisms.  B.  Sepa- 
rated prisms  seen  lengthwise.  (Carpenter.) 

the  prism  into  as  many  somewhat  cubical  sections  as 
there  are  areas  occupied  by  these  minute  cross-lines. 
These  prisms  are  separated  from  each  other  by  a 
small  amount  of  cement-substance.  When  the  enamel 
begins  to  form,  the  enamel-cells  lengthen  towards  the 
dentine.  The  lengthened  portion  soon  becomes  cal- 
cified, the  calcareous  deposit  first  appearing  at  the 
sides  of  the  prism,  or  in  the  intercellular  cement. 
After  the  calcification  of  the  newly-formed  end  of  the 
columnar  enamel-cell  has  measurably  progressed,  the 
dentinal  end  of  the  cell  again  lengthens,  and  this 
new  portion  of  the  cell  is  in  its  turn  calcified.  This 
process  repeats  itself,  until  the  original  columnar 
enamel-cell  is  much  lengthened,  and  the  whole  is 


gradually  converted  into  successive  sections  of  the 
enamel-prism.  It  is  this  successive  periodic  trans- 
formation of  the  enamel-cell  into  calcified  prisms 
which  gives  to  the  latter  the  peculiar  appearance 
shown  in  B,  Fig.  33. 


MUSCLE. 

Muscular  tissue  comprises  two  general  varieties, 
unstriped  or  smooth,  and  striated.  The  elements  of 
this  tissue  are  derived  from  the  mesoblast,  and  are 
well  supplied  with  capillary  vessels  and  nerves. 

SMOOTH  OR  UNSTRIPED  MUSCLE. 

This  variety  of  muscular  tissue  is  composed  of 
spindle  or  fusiform  cells,  whose  transverse  diameter  is 
usually  small  in  proportion  to  the  length  of  the  long 
axis  of  the  cell.  These  cells  are  soft,  and  are  often  more 
or  less  prismatic  from  mutual  pressure.  They  may 
occur  more  or  less  isolated,  but 
are  usually  collected  into  bun- 
dles. The  cells  constituting 
the  bundles  are  closely  packed 
together,  the  spindle  extremity 
of  one  cell  fitting  between  the 
bellies  of  two  or  more.  These 
closely  -  packed  muscle -cells 
are  slightly  separated  from 
each  other  by  a  small  amount 
of  intercellular  cement,  appa- 
rently similar  to  that  which 
unites  the  cells  of  epithelial 
surfaces.  In  this  albuminous 
intercellular  cement  are  often 
found  a  small  number  of  flat, 
connective-tissue  cells,  more 
or  less  branched,  and  some- 
times a  very  few  scattered,  de 


Fig.  34. 


SMOOTH  OR  UNSTRIPEDMUSCU- 
LAR-FlBRE-CELLS  FROMAHTERIES 
[  HUM  AS]. — 1.  From  the  popliteal 
artery.  A,  without,  B,  with 
acetic  acid.  2.  From  a  branch 
of  the  anterior  tibial ;  a?  rod- 
shaped  nuclei  of  the  fibres.  Mag- 
nified 350  diamters.  (Gray.) 


licate  connective  fibres.  This 
intercellular  material  corresponds  to  the  endomysium 
of  striped  muscles. 

Arrangement  and  distribution  of  smooth  muscle- 
fibres. — The  muscular  bundles  thus  composed  are  sep- 
arated by  a  variable  quantity  of  ordinary  loose  con- 
nective-tissue— an  analogue  of  the  perimysium  sur- 
rounding bundles  of  striped  muscles.  The  bundles 
of  smooth  muscles  may  anastomose  with  each  other 
so  as  to  form  a  regular  muscular  network.  Such  a 
muscular  network  may  be  spread  out  with  a  fenes- 
trated  layer.  Frequently  the  bundles  are  placed  side 


II I S  T  O  L  0  G  Y. 


by  side  to  form  continuous  muscular  membranes, 
or  they  may  be  collected  into  large  bundles  or  cords. 
Besides  the  familiar  locations  in  which  smooth  muscle- 
fibres  are  present,  such  as  the  muscular  coat  of  the 
intestine,  the  walls  of  arteries,  veins,  and  large  lym- 
phatic trunks,  the  iris  and  ciliary  body,  etc.,  they  are 
also  found  around  the  ducts  of  glands  and  sometimes 
in  the  loose  connective-tissue  between  their  acini,  in 
the  infundibula  of  the  lungs,  in  the  fibrous  trabeculas 
of  the  spleen,  sometimes  in  the  trabecula?  of  lymph- 
glands  of  the  lower  animals,  and  in  many  other 
places. 

Form  and  minute  structure  of  smooth  muscle- fibres. — 
The  spindle-cell  of  smooth  muscle  is  sometimes 
branched  at  the  extremity.  The  largest  cells  are 
found  in  the  pregnant  uterus  near  term,  the  smallest 
occur  around  the  ducts  of  sweat-glands. 

The  minute  structure  of  the  smooth,  fully-devel- 
oped muscle-cell  consists  externally  of  a  very  delicate, 
scarcely  visible,  enveloping  membrane,  which  seems 
to  be  of  an  elastic  hyaline  construction.  Within 
this  delicate  membrane  is  inclosed  the  cell-body  and 
nucleus.  The  body  of  the  cell  consists  of  a  soft,  gela- 
tinous substance,  in  which  are  imbedded  a  number  of 
fine  fibrils.  These  fine  fibrils  run  in  the  direction  of 
the  long  axis  of  the  cell,  and  when  the  element  is 
seen  longitudinally  give  it  a  delicate,  longitudinal 
striation.  The  nucleus  is  generally  more  or  less  rod- 
shaped,  and  is  located  near  the  middle  of  the  cell. 
It  is  limited  by  a  thin  envelope  of  double  contour, 
and  contains  one  or  more  small  nucleoli.  Within  the 
nucleus  is  a  close  reticulum  of  fine  fibrils,  which,  at 
the  two  extremities  of  the  nucleus,  are  in  connection 
with  the  fibrils  of  the  cell-body. 

Seen  in  transverse  section,  if  the  cut  passes  through 
at  the  level  of  the  nucleus,  the  latter  offers  a  circular 
outline  near  the  centre  of  the  cross-cut  of  the  cell, 
which  itself  now  appears  more  or  less  circular  or 
polyhedral.  In  transverse  sectioa  the  cell-body  ap- 
pears dotted  with  fine  points — the  cross-cuts  of  the 
longitudinal  fibrils  above  mentioned.  Smooth  muscle- 
fibres,  when  isolated  and  examined  fresh,  sometimes 
present  little  thickenings  in  their  course,  causing  a 
slight  moniliform  outline  of  the  element  when  seen 
longitudinally.  These  swellings  are  supposed  to  be 
due  to  irregular  contractions  of  the  substance  of  the 
fibre.  Over  the  position  of  these  slight  swellings 
the  thin  enveloping  membrane  is  often  thrown  into 
minute  transverse  folds  or  ridges.  These  occasional 
ridges  of  the  membranous  envelope  of  the  smooth 
muscle-cell  frequently  give  to  the  latter  an  apparent 
interrupted  transverse  striation. 


STRIATED  MUSCLE. 

The  voluntary  muscles,  namely,  those  which  move 
the  skeleton,  the  tongue,  the  pharynx,  the  upper  part 
of  the  oesophagus,  and  some  involuntary  muscles,  as 
for  example  the  heart,  and  the  diaphragm,  are  com- 
posed of  muscular  fibres,  which,  when  fully  formed, 
are  striated,  or  striped.  This  form  of  muscular  tissue 
is  usually  red  or  flesh  color,  while,  on  the  contrary, 
the  smooth  muscular  tissue  is  ordinarily  quite  pale. 

Muscular  bundles. — Striated  muscles  are  composed 
of  aggregations  of  very  fine  striated  fibres,  imbedded 
in  a  connective-tissue  framework,  which  carries  the 
necessary  vessels  and  nerves.  The  muscle-fibres  have 
certain  relations  to  this  connective-tissue  framework, 
as  well  as  to  each  other.  The  smallest  striped  mus- 
cles consist  of  a  greater  or  lesser  number  of  striated 
muscle-fibres  (primitive  fibres),  running  parallel  to 
each  other,  and  closely  packed  together  to  form  a 
primary  bundle.  The  primitive  fibres  during  life  are 
soft,  and  capable  of  assuming  outlines  due  to  mutual 
pressure.  Between  these  more  or  less  closely- packed 
primitive  muscle-fibres,  and  separating  as  well  as 
holding  them  together,  is  a  certain  amount  of  semi- 
fluid, albuminous  cement-substance,  in  which  are  to 
be  found  a  few  delicate  connective-tissue  fibrils,  and 
here  and  there  a  flat,  perhaps  branched,  connective- 
tissue  corpuscle  (figs.  2,  3,  Plate  VI.).  Occasionally 
in  this  interfibrous  tissue  we  see  also  some  large, 
granular  plasrnatic  cells  of  Waldcyer,  flattened  be- 
tween the  primitive  fibres.  In  this  scant  framework 
ramify  small  nerves  and  capillary  vessels. 

Endomysium  and  perimysium. — This  delicate  inter- 
fibrous  tissue  is  known  as  the  endomysium.  It  is  in 
connection  with  the  perimysium,  a  name  reserved  for 
the  connective-tissue  which  surrounds  the  primary 
bundles.  When  several  primary  muscular  bundles 
are  bound  together  to  form  a  larger  muscle,  we  have 
a  secondary  bundle  formed.  In  the  perimysium  or  tis- 
sue surrounding  the  secondary  bundles  we  have  all 
the  characteristics  of  loose  connective-tissue.  Even  the 
presence  of  adipose  vesicles  may  be  noted,  and  arteri- 
oles  and  venules  are  quite  frequent,  as  well  as  the  cor- 
responding lymphatics.  In  the  larger  muscles  of  the 
bodjr,  we  meet  with  tertiary  muscle-bundles,  to  form 
which  a  number  of  secondary  bundles  are  bound  to- 
gether within  a  common  sheath. 

Muscle-fibres.  —  The  primitive  muscle-fibre,  when 
not  influenced  by  lateral  pressure,  is  usually  some- 
what cylindrical  in  form.  Its  length  is  exceedingly 
great  in  comparison  to  the  width  of  its  cross-sec- 
tion. In  small,  short  muscles,  it  is  possible  that 


MUSCLE. 


65 


each  primitive  muscle-fibre  may  extend  the  whole 
length  of  the  muscle.  The  longer  and  larger  muscles 
are  probably  composed  by  many  lengths  of  fibres 
whose  ends  overlap.  It  is  believed  by  some  authors 
that  in  such  muscles  no  primitive  fibre  ever  ex- 
ceeds a  length  of  one  and  a  half  or  two  inches.  Near 
their  extremities  the  muscle-fibres  taper  off'  to  a  more 
or  less  sharp  conical  point.  The  fibre  is,  therefore, 
somewhat  spindle-shaped,  and  has  a  variable  diameter 
according  to  the  part  selected.  As  in  the  fusiform 
smooth  muscle-cells,  the  tapering  extremity  of  one 
fibre  is  inserted  between  the  thicker  portions  of  two 
or  more  adjacent  fibres.  A  cross-section  of  a  muscu- 
lar bundle  composed  of  such  an  arrangement  of 
primitive  fibres  will  necessarily  show  fibres  appa- 
rently of  a  widely  varying  diameter.  While  there 
are  some  actual  variations  in  the  size  of  the  several 
primitive  fibres  which  constitute  a  given  muscular 
bundle,  yet  in  a  muscle  which  is  not  rapidly  changing, 
the  muscle-fibres  have  a  very  uniform  diameter. 
The  average  diameter  of  striped  muscle-fibres,  how- 
ever, not  only  differs  enormously  in  different  species 
of  animals,  but  it  also  varies  considerably  between 
different  muscles  in  the  same  animal. 

Form  and  structure  of  muscle-fibres. — The  striped 
muscle-fibre  is  nearly  always  unbranched,  but  in 
human  striated  muscles  we  find  some  examples  of 
branched  fibres,  as  in  the  tongue,  in  some  of  the  facial 
muscles,  and  in  the  heart.  In  the  latter  organ  the 
branched  fibres  unite  to  form  a  genuine  muscular 
retioulum.  The  peculiarities  of  the  cardiac  muscle 
will  be  considered  later. 

When  a  striped  muscle-fibre  is  examined  under  the 
microscope  during  life,  it  is  at  first  a  gray  and  appa- 
rently nearly  homogeneous  cylinder.  Soon  after  re- 
moval from  the  relations  in  which  it  naturally  exists, 
it  begins  to  show  a  faint  segmentation  into  alternate 
dark  and  light  cross-bands  of  unequal  thickness. 
During  a  state  of  contraction  of  the  fibre  the  dark 
bands  are  narrowest ;  in  elongation  of  the  fibre  the 
dark  bands  reach  their  greatest  width.  The  reverse 
is  true  of  the  light  bands. 

Contractile  disks. — The  action  of  hydrochloric  acid 
upon  the  fibres  causes  them  to  be  readily  broken  up 
into  a  countless  number  of  thin  transverse  disks 
piled  one  upon  another  like  rouleaux  of  coins.  (See  3, 
fig.  1,  Plate  VI.)  When  the  transverse  marking  into 
alternate  bands  of  light  and  dark  substance  makes  its 
appearance  in  fresh  muscle,  the  fibres  present  the  as- 
pect shown  in  A,  Fig.  35,  when  examined  under  a 
magnifying  power  of  700  or  800  diameters.  The 


dark  bands  have  been  called  contractile  disks,  the  light 
bands  interstitial  disks. 

Sarcous  elements. — Sooner  or  later  after  the  removal 
of  the  fibre  from  its  normal  surroundings  the  dark  con- 
tractile disks  begin  to  show  extremely  narrow  light 
lines  which  run  vertically  and  divide  the  tissue  into  a 


Fig.  35. 


B 


STRIATED  MCSCOLAR  FIBRE  [HUMAN].— A.  Portion  of  a  medium-sized  muscu- 
lar fibre,  magnified  nearly  800  diameters.  B.  Separated  bundles  of  fibrils, 
equally  magnified,  a  a,  larger,  and  b  b,  smaller  collections;  c,  still  smaller  ; 
d  d,  the  smallest  which  could  be  detached.  (Gray.) 

large  number  of  short  rod-like  elements  of  a  dark  ma- 
terial. Under  these  conditions  each  disk  appears  to 
be  constituted  by  a  single  row  of  alternating  light  and 
dark  lines  extending  parallel  to  the  axis  of  the  mus- 
cle-fibre. The  minute  dark  rods  of  which  each  con- 
tractile disk  is  composed  are  regarded  as  the  ultimate 
contractile  units,  and  are  known  as  the  sarcous  elements 
of  Bowman.  They  lengthen  during  elongation  of  the 
fibre,  and  shorten  and  increase  in  thickness  during 
contraction.  When  the  successive  contractile  disks  of 
a  muscle-fibre  are  differentiated  into  these  alternate 
light  and  dark  lines  parallel  to  the  axis  of  the  fibre, 
the  optical  effect  produced  is  that  of  a  longitudinal 
striation,  for  the  ends  of  the  dark  rods  of  one  con- 
tractile disk  are  placed  vertically  above  or  below 
those  of  adjacent  disks.  Very  frequently,  indeed,  the 
longitudinal  and  the  transverse  striations  are  simulta- 
neously visible  in  the  same  fibre.  Certain  reagents 
have  the  effect  of  bringing  out  the  one  form  of  striation 
more  distinctly  than  the  other.  Thus  alcohol  usually 
makes  the  longitudinal  striation  quite  prominent, 
while  on  the  contrary  hydrochloric  acid  accentuates 
the  transverse  strias. 


66 


HISTOLOGY. 


&',  Fig.  36,  gives  a  vertical  view  of  a  transverse  disk 
after  the  latter  has  been  differentiated  into  its  ulti- 

Fig.  36. 


FRAHMESTB  OF  STRIPED  EI.BMBXTARY  FIBRES,  showing  a  cleavage  in 
opposite  directions.  High  power. — A.  Longitudinal  cleavage.  The  longi- 
tudinal and  transverse  lines  are  both  seen.  Some  longitudinal  lines  are  darker 
and  wider  than  the  rest,  and  are  not  continuous  from  end  to  end.  This  results 
from  partial  separation  of  the  fibrillx.  c.  Fibrillaj  separated  from  one  another 
by  violence  at  the  broken  end  of  the  fibre,  and  marked  by  transverse  lines, 
c',  c".  Two  appearances  commonly  presented  by  the  separated  single  fibrills 
more  highly  magnified.  At  c'  the  borders  and  transverse  lines  are  all  perfectly 
rectilinear,  and  the  included  spaces  perfectly  rectangular.  At  c"  the  borders 
are  scalloped  and  the  spaces  bead-like.  When  most  distinct  and  definite,  the 
fibrilla  presents  the  former  of  those  appearances.  B.  Transverse  cleavage.  The 
longitudinal  lines  are  scarcely  visible,  a.  Incomplete  fracture  following  the  op- 
posite surfaces  of  a  disk,  which  latter  stretches  across  the  interval,  and  retains 
the  two  fragments  in  connection.  The  edge  and  surfaces  of  this  disk  are  seen  to 
be  minutely  granular,  the  granules  corresponding  in  size  to  the  thickness  of  tho 
disk,  and  to  the  distance  between  the  faint  longitudinal  lines,  b.  Another 
disk  nearly  detached,  b'.  Detached  disk  (more  highly  magnified),  showing 
the  sarcous  elements.  (Gray.) 

mate  sarcous  elements,  by  the  action  of  some  reagent 
which  has  softened  or  dissolved  the  interstitial  sub- 
stance between  them. 

Fields  of  Cohnheim. — If  a  perfectly  fresh  and  living 
muscle  is  frozen,  and  cut  into  thin  transverse  sections, 
and  immediately  examined  under  a  high  magnifying 
power,  the  following  appearances  are  noted  :  At  first 
the  surface  of  the  section  is  uniformly  gray.  Very 
soon  the  field  begins  to  be  mottled.  The  surface  is 
now  everywhere  marked  by  fine  brilliant  lines  which 
cross  each  other  in  such  a  manner  as  to  form  an 
irregular  bright  network  inclosing  darkish-gray  areas. 
The  dark-gray  areas  are  the  ends  of  the  ultimate 
sarcous  elements  or  the  dark  rods  seen  as  above 
stated  when  the  longitudinal  fibrillation  becomes 
apparent.  The  light  lines  correspond  to  sections 
of  the  bright  substance  between  the  dark  rods. 
The  width  of  the  bright  lines  mottling  the  gray 
field  gradually  increases  a  little  during  the  obser- 
vation, while  at  the  same  time  the  dark  areas  limited 
by  the  meshes  correspondingly  lessen  in  extent.  The 
dark  areas  are  the  so-called  fields  of  Cohnheim.  The 
central  object  in  Fig.  37  very  well  represents  the  ap- 
pearance above  described,  although  it  was  intended 
merely  to  show  the  manner  of  termination  of  a  nerve. 
The  dark  areas  or  fields  of  Cohnheim  are  dotted  with 


extremely  fine  points.  These  are  the  ends  of  fine 
fibrils  which  can  be  observed  in  the  sarcous  elements 
when  the  latter  are  seen  longitudinally  under  favor- 
able conditions.  Various  reagents  which  effect  the 


7. 


TRANSVERSE  SECTION  OF  ONE  OF  THE  MUSCLES  OF  Tin;  THIOH  op  THE  LACEETA 
AGILIS  (A  COMMON  EUROPEAN  LIZARD),  made  whilst  frozen,  and  magnified  400 
diameters. — N.  Nerve  of  a  muscle-fibre  which  is  surrounded  by  portions  of  six 
others,  a.  Nucleus  of  tho  nerve-sheath,  b.  Nucleus  of  the  sarcolemma.  c.  Sec- 
tion of  nucleus  of  terminal  plate  of  nerve,  d.  Transverse  section  of  terminal  plate, 
surrounded  by  granular  material,  e.  Transverse  section  of  muscle-nuclei.  /. 
Fine  fat-drops.  The  angular  dark  particles  are  sections  of  groups  of  sarcous 
elements.  ( Carpenter.) 


death  of  the  constituents  of  the  muscle-fibre  cause 
the  sarcous  elements  to  shrink  from  each  other  and 
leave  proportionately  large  spaces  between  them, 
which  are  filled  with  an  interstitial  cement-substance 
—the  light  network  seen  in  transverse  sections,  and 
the.light  lines  observed  between  the  rod-shaped  sar- 
cous elements  when  the  fibre  is  viewed  lengthwise. 

Sarcolemma,  intermediate  disks,  etc. — The  muscle- 
fibre  is  more  or  less  closely  enveloped  in  a  thin, 
tough,  elastic,  apparently  hyaline  sheath — the  sarco- 
lemma. This  elastic  tube  is  partitioned  across  at  short, 
regular  intervals  by  thin  plates  which  are  offshoots 
from  the  inner  wall  of  the  sarcolemma.  Such  plates 
consist  of  substance  somewhat  similar  to  that  of  the 
sarcolemma,  but  are  not  so  tough  and  resistant.  They 
cross  the  tube  through  the  middle  of  the  light  or 
interstitial  disk,  and  are  known  as  the  membranes  or 
intermediate  disks  of  Krause  (z,  Fig.  38). 

The  intermediate  disks  of  Krause,  therefore,  divide 
the  tube  formed  by  the  sarcolemma  into  cylindrical 
sections,  placed  end  to  end.  Each  of  these  cylindrical 
sections  contains  a  dark  contractile  disk,  with  a  half 
of  an  interstitial  disk  above  and  below,  separating 
it  from  the  intermediate  disks  of  Krause.  In  each 
half  of  the  light  interstitial  disk  is  frequently 
found  a  thin  transverse  layer  of  somewhat  dark  sub- 
stance which  separates  into  granules  when  the  dark 
contractile  disk  shows  a  division  into  sarcous  ele- 
ments. This  thin  layer  of  dark  substance  has  been 


MUSCLE. 


67 


called  the  secondary  or  collateral  disk  (n,  Fig.  38).     It 
requires  strong  and  well-defining  lenses  for  the  demon- 
stration of  these  details  of  the  structure  of  muscle- 
Fig.  38. 


n 

-  x, 


STRUCTURE  OF  STRIATED  MUSCULAR  FIBRE,  AFTER  ENRELMANX,  FROM  TEI.E- 
PIIORl'3  MELANITRU3  (A  COMMON  EUROPEAN  BEETLE).  CUTANEOl'3  MUSCLE 
FROM  THK  ABDOMEN. — ni.  Median  disk.  n.  Secondary  disk.  z.  Intermediate 
ilisk.  Magnified  1000  diameters.  The  sarcolemma  U  seen  ou  the  left  side. 


fibres.  Engelmann  and  Henscnn  have  each  recorded 
the  presence,  in  the  middle  of  the  transverse  or  con- 
tractile disk,  of  a  transverse,  lighter  band  which  they 
have  called  the  median  disk  (diagrammaticallv  shown 
at  TO,  Fig.  38).  The  above-described  dark  elements 
of  the  striped  muscle  have  been  found  to  be  doubly 
refracting;  they  consequently  polarize  light,  while 
the  light  substance  which  separates  them  has  not  a 
similar  effect  upon  the  luminous  rays. 

The  shortening  and  transverse  thickening  of  the 
dark  rods  or  sarcous  elements  of  the  contractile  disk, 
which  takes  place  during  contraction  of  the  fibre, 
causes  the  interstitial  substance  to  apparently  increase 
in  amount.  Since  the  thickened  rods  are  then  more 
closely  pressed  together,  the  fluid  portion  of  the  in- 
terstitial substance  must  necessarily  be  squeezed  out 
above  and  below,  and  increase  the  volume  of  the  half 
of  the  light  or  interstitial  disk  above  and  below  the 
contractile  disk.  Frequently  a  part  of  this  expressed 
interstitial  substance  finds  its  way  between  the  sarco- 
lemma and  the  edge  of  the  contractile  disk,  and  sepa- 
rates the  two,  thus  producing  a  convexity  or  bulging 
of  the  sarcolemma  at  these  points.  This  condition  is 
shown,  somewhat  diagram matically  on  the  left  in  Fig. 
38.  Sometimes  the  attachment  of  the  intermediate 
disk  of  Krausc  to  the  sarcolemma  breaks,  either  from  a 
destructive  process  at  work  in  the  fibre  itself,  or  from 
the  action  of  reagents  which  soften  the  intermediate 
disk  and  cause  the  substance  of  the  light  interstitial 
disk  to  swell  greatly.  The  sarcolemma  may  then  be 
separated  from  the  surface  of  the  muscle-fibre  for  a 
considerable  part  or  the  whole  of  its  length.  Occa- 
sionally the  muscle-fibre  may  suffer  a  transverse  frac- 
ture within  the  sarcolemma.  A  retraction  of  each 
fragment  then  takes  place,  resulting  in  their  separa- 
tion. Such  a  condition  is  shown  in  i,  fig.  1,  Plate  VI. 


Theensheathing  sarcolemma  remaining  unbroken  be- 
comes wrinkled,  and  perhaps  twisted,  as  is  seen  at  n, 
1,  in  the  figure  last  mentioned.  These  fractures  in- 
variably pass  through  the  light  or  interstitial  disk. 

The  interstitial  substance  between  the  sarcous  ele- 
ments often  contains,  especially  in  the  lower  animals, 
minute  molecules,  sometimes  of  pigment,  sometimes 
of  fat — the  interstitial  granules  of  Kolliker. 

Muscle-corpuscles. — Besides  the  constituents  above 
enumerated,  striped  muscle-fibres  contain,  at  more  or 
less  scattered  intervals,  cellular  elements  which  ap- 
pear to  be  closely  analogous  to  connective-tissue  cor- 
puscles. In  nearly  all  the  muscles  of  most  of  the 
higher  animals,  these  elements  rest  upon  the  surface 
of  the  muscle-fibre,  and  form  a  part  of  it.  They  are 
not  connected  with  the  sarcolemma.  In  some  of  the 
Amphibia,  these  cells  are  scattered  through  the  sub- 
stance of  the  fibre  (see  e,  Fig.  37).  In  birds  they 
are  found  in  both  locations.  In  the  muscle  of  the 
heart  of  man  they  exist  near  the  centre  of  the 
fibre.  When  in  the  depth  of  the  fibre,  they  are  im- 
bedded in  the  interstitial  substance,  and  they  consist 
of  a  flattened  oval  nucleus,  containing  one  or  more 
nucleoli,  the  long  axis  running  parallel  with  the 
length  of  the  fibre.  In  the  adult,  fully-matured, 
normal  muscle-fibre,  the  nucleus  is  surrounded  by  a 
very  small  amount  of  protoplasm,  which  is  more  ex- 
tensive at  the  ends  of  the  oval  nucleus,  where  it  is 
frequently  lengthened  out  into  a  tapering  extremity. 
The  broad  surface  of  the  cell  then  presents  a  some- 
what fusiform  outline.  When  seen  in  profile  the  out- 
line appears  more  linear.  The  protoplasm  usually 
contains  a  certain  number  of  dark,  or,  sometimes, 
shining  granules,  mostly  aggregated  at  the  -poles  of 
the  cell. 

These  cells  are  known  as  muscle-corpuscles.  Their 
office  has  been  variously  interpreted.  Some  have 
thought  them  to  be  the  terminal  organs  of  the  nerves, 
which  supply  the  fibre.  Others  have  regarded  them 
as  simple  connective-tissue  corpuscles.  The  weight 
of  opinion,  however,  seems  to  support  the  view  that 
they  are  the  builders  of  the  muscle-fibres.  The  rela- 
tion which  they  bear  to  the  growth  of  muscle  will 
be  considered  when  we  speak  of  its  development. 

Cardiac  muscle -fibres. — In  the  heart  of  man  the 
muscle-fibres  possess  certain  peculiarities.  In  the 
first  place  they  seem  to  be  destitute  of  an  investing 
sarcolemma.  In  the  second  place  they  are  very 
short,  and  are  branched  in  the  manner  shown  in  Fig. 
39.  Each  fibre  possesses  one  or  more  nuclei,  which 
are  imbedded  in  the  depth  of  the  fibre.  The  end  of 
a  branch  of  one  fibre  abuts  against  the  end  of  that 


HISTOLOGY. 


of  another.      In    this   way   an    anastomosis   of   the 
branched    muscle-fibres    is    formed.      When    heart- 
Fig.  39. 


ASASTOMOSINQ  Mcscr.E-FlBREs  op  THE  HEART,  seen  in  a  longitudinal  section. 
On  the  right  tho  limits  of  the  separate  cells  with  their  nuclei  ure  exhibited 
somewhat  diagrammatical ly.  (Gray.) 

muscle  is  cut  transverse  to  the  direction  of  the 
muscle-fibres,  instead  of  the  cross-section  of  the  fibre 
presenting  a  circular  outline,  as  in  ordinary  striped 
muscle,  it  is  often  elongated.  This  is  the  case  when 
the  cut  has  passed  through  the  body  of  the  fibre  near 


the  point  where  it  branches.  Because  of  the  extreme 
shortness  of  the  branched  muscle-fibres  almost  every 
one  of  them  in  the  cross-section  is  seen  to  contain 
near  its  centre  a  muscle-corpuscle. 

Termination  of  muscle  fibres.  —  As  has  already 
been  mentioned,  each  individual  muscle-fibre  termi- 
nates in  a  tapering  conical  extremity.  Whether 
these  extremities  end  in  tendon,  or  in  the  depth  or 
body  of  the  muscle,  in  the  endoinysium  between  the 
muscle-fibres  of  tho  primary  bundles,  they  are  at- 
tached to  connective-tissue  fibres  (t,  2,  fig.  1,  Plate 
VI.).  It  seems  to  be  still  unsettled  exactly  how 
this  connection  is  established. 

Unless  the  tissue  is  especially  prepared  for  exami- 
nation, the  longitudinal  tibrillas  appear  to  be  directly 
continuous  at  their  extremity  with  the  connective- 
fibres,  and  the  one  seems  to  pass  insensibly  into  the 
other.  Perhaps  such  a  simple  connection  may  really 
exist  in  many  instances;  but  it  is  probable  that,  in 
most  cases,  where  muscle  is  inserted  into  tendon,  there 
is  a  different  mode  of  communication.  The  sarco- 
lemma  probably  continues  without  interruption  around 
the  conical  end  of  the  muscle-fibre,  and  at  this  point 
is  attached  by  its  external  surface  to  the  bundles  of 
fibrous  tissue  which  form  the  tendon.  Whether  the 


EXPLANATION  OF  PLATE  VI. 


Fig.   1.     The   appearances   of  striated  muscle-fibres    after 
varied  treatment.     Moderate  power.     (Frey.) 

1.  A  muscle-fibre  (m)  ruptured  at  n,  showing  the  sheath 
or  sarcolemma  partly  emptied  and  twisted. 

2.  The  end  of  a  muscle-fibre  from  the  biceps  of  Man,  m  ; 
a   fibrous  bundle,  t,  of  the  interstitial   connective-tissue   is 
attached  to  its  pointed  extremity. 

3.  A  Human  muscle-fibre  after  prolonged  treatment  with 
hydrochloric  acid.       It   can   now  be   readily  split   up   into 
transverse  disks,     n,  nucleus  of  muscle-corpuscles. 

4.  A  muscle-fibre  from  the  leg  of  a  Frog  after  protracted 
treatment  with  dilute  hydrochloric  acid.     From  the  cut  end, 
t,  very  fine  fibres,  upon  which  minute  granules  are  distrib- 
uted, are  seen  projecting. 

Fig.  2.  Transverse  section  of  Human  biceps.    High  power. 

(After  Frey.) 

m,  Muscle-fibres,  cut  across  ;  v,  a  section  of  a  bloodvessel ; 
e,  a  fat  vesicle  in  the  interstitial  connective-tissue. 

Fig.    3.    Fragment  of  sartorius  muscle  of  a  Frog.     High 

power.     (After  Ranvier.) 
n,  Nuclei  of  muscle-corpuscles,  seen  partly  in  face. 


Fig.  4.  Muscle-bundle  of  the  dorsal  fin  of  the  Hippocampus 
(a  fish   commonly  known   as   the   sea-horse),  showing 
method   of  attachment    of  the   fibrous    bundle   of  the 
tendon.     High  power.     (After  Ranvier.) 
m,  Muscle-fibres  ;  at  t  they  are  attached  to  the  tendon- 
fibres   through   the   intermediation    of    a    double-contoured 
membrane,  which  is  continuous  with  the  elastic  sheath  (n) 
of  the  bundle. 

Fig.  5.  Highly-magnified  capillary  bloodvessel,  after  injec- 
tion with  a  weak  solution  of  nitrate  of  silver,  and  sub- 
sequent staining  with  picrocarminate  of  ammonia.  The 
dark  lines  mark  out  the  boundaries  of  the  endothelial 
cells  forming  the  wall  of  the  vessel;  the  nuclei  are  also 
distinctly  seen.  (Ranvier.) 

Fig.  C.  Shows  a  capillary  bloodvessel,  surrounded  by  and 
attached  to  the  fibres  of  the  reticular  tissue.  (Ran- 
vier.) 

c,  The  capillary ;  r,  the  reticular  fibres ;  n,  nuclei  of  flat 
endothelial  cells  upon  the  reticular  fibres. 


PLATE    VI 


n-  ni 


Fig .4. 


Fig   5. 


Fig    6 


Fig. 3. 


BLOODVESSELS. 


69 


fibres  of  the  tendon  are  inserted  into  the  sarcolemma 
at  this  point,  or  are  simply  glued  upon  its  exterior 
surface  by  the  intervention  of  a  tough,  stieky  mate- 
rial, has  not  yet  been  determined.  Fig.  4,  Plate  VI., 
represents  such  a  mode  of  insertion  of  a  muscle-fibre 
into  tendon.  The  preparation  from  which  the  draw- 
ing was  made  is  from  the  large  dorsal  fin  of  the  Hip- 
pocampus,  or  sea-horse.  But  the  artist  has  failed  to 
show  distinctly  the  most  important  feature  of  the 
preparation.  At  t,  where  the  muscle- fibre  ends  in  the 
tendon,  the  line  between  the  two  should  have  a  double 
contour,  and  be  continuous  with  the  double-contoured 
line  representing  the  sarcolemma  ensheathing  the 
muscle-fibre. 

DEVELOPMENT  OF  MUSCLE. 

Muscular  tissue  is  developed  from  the  cells  of  the 
middle  or  connective-tissue  layer  of  the  blastoderm. 
The  fibres  of  striped  muscles  originate  in  the  follow- 
ing manner:  A  fusiform  cell  in  the  connective-  or 
gelatinous  tissue  of  the  embryo  suffers  a  division  of 
its  nucleus.  The  two  new  nuclei  divide  again,  and 
this  process  continues  until  the  original  uni-nucleated 
spindle-cell  has  become  more  or  less  completely  filled 
with  a  number  of  nuclei  arranged  in  a  linear  series 
from  one  end  of  the  cell  to  the  other.  Proceeding 
equally  with  this  increase  of  nuclei,  the  cell  thickens 
somewhat,  and  greatly  elongates.  Here  and  there 
the  cell-body  soon  begins  to  show  cross-markings — - 
the  earliest  appearance  of  the  transverse  disks.  This 
transformation  of  the  cellular  protoplasm  into  the  con- 
tractile elements  of  the  full-grown  muscle  continues 
to  spread  throughout  the  fusiform  cell-body,  until 
nearly  the  whole  of  the  latter  becomes  transversely 
striated.  The  protoplasm  immediately  surrounding 
the  nucleus  is  the  last  to  experience  this  metamor- 
phosis. 

Even  in  the  full-grown  and  adult  fibre  a  small  por- 
tion of  the  original  protoplasm  remains  around  the 
nucleus,  and  constitutes,  with  the  latter,  the  muscle- 
corpuscle  above  described.  It  is  not  yet  known 
whether  the  sarcolemma  is  the  product  of  an  excre- 
tion by  the  protoplasm  of  the  rnuscle-ccll,  or  whether  it 
is  a  formation  from  the  surrounding  connective-tissue. 

Reproduction  of  muscle  fibres. — In  various  muscles  of 
the  human  organism  are  many  striped  fibres  contain- 
ing a  very  large  number  of  muscle-corpuscles,  sur- 
rounded by  a  proportionately  large  quantity  of  proto- 
plasm, and  presenting  other  evidences  of  growth.  It 
is  probable  that  in  health  there  is  a  continual  destruc- 
tion and  reproduction  of  muscle-fibres.  It  is  certainly 
so  in  many  diseases. 


BLOODVESSELS. 

The  blood  of  man  flows  throughout  the  body  in  a 
system  of  channels,  which,  according  to  their  size, 
construction,  and  the  character  of  the  blood  passing 
through  them,  are  denominated  arteries,  veins,  capil- 
laries, sinuses. 

Each  of  these  species  of  bloodvessels  has  a  char- 
acteristic structure  which  generally  differentiates  it 
from  all  the  others.  But  while  there  is  a  general 
plan  of  construction  common  to  the  members  of  each 
species,  there  are  slight  differences  which  constitute 
varieties.  Some  of  these  variations  will  be  incident- 
ally noted. 

Capillaries.  —  The  simplest  form  of  bloodvessel 
met  with  in  man  is  the  blood -capillary  —  an  ex- 
tremely minute  tube.  The  most  primitive  form  of 
the  capillary  is  that  of  a  simple  cylindrical  channel 
hollowed  out  in  the  connective-tissue,  with  no  other 
definite  wall  than  that  of  a  delicate,  elastic,  limiting 
membrane,  consisting  of  a  single  complete  layer  of 
flat,  thin,  elastic,  endothelial  plates,  such  as  have 
already  been  described  as  covering  serous  surfaces. 
Each  of  these  endothelial  plates  contains  one,  some- 
times two,  flattened  ovoid  nuclei.  Under  favorable 
conditions  intra-nuclcar  and  intra-cellular  networks 
can  be  demonstrated  in  these  cells.  Staining  by 
nitrate  of  silver  and  exposure  to  light  blackens  the 
intercellular  cement  between  their  edges,  which  are 
normally  in  apposition  with  edges  of  the  adjacent 
endothclia,  and  if  the  preparation  is  subsequently 
stained  with  carmine  the  nuclei  show  a  brilliant  red. 
The  capillary,  of  which  fig.  5,  Plate  VI.,  is  a  very 
faithful  drawing,  has  been  treated  in  this  manner. 
The  outlines  of  the  cells  are  shown  deep  black  upon 
the  top  of  the  capillary  cylinder,  and  by  dotted  lines 
on  the  bottom  portion.  The  cells  are  seen  to  be  more 
or  less  lozenge  shaped,  with  the  long  axis  of  the  cell 
running  with  the  length  of  the  capillary.  The  edges 
of  cells  are  observed  to  be  sinuous.  The  sinuosity 
of  the  edges  of  the  cells  is  much  lessened  when  the 
capillaries  are  distended.  Lender  the  influence  of 
irritation  or  inflammation  the  endothelia  swell 
up.  Their  edges  then  become  separated  at  points, 
thus  forming  openings  in  the  capillary  wall.  The 
smallest  of  these  are  called  stigmata,  the  largest  sto- 
mata.  Probably  it  is  through  these  openings  that  the 
elements  of  the  blood  escape  during  inflammation. 
According  to  some  authors,  they  are  in  direct  com- 
munication with  the  lymph-spaces  of  the  surrounding 
connective-tissue. 


70 


HISTOLOGY. 


A  little  more  complex  form  of  the  blood-capillary 
consists  of  an  addition  to  the  vessel  of  an  incomplete 
sheath  of  fusiform  or  stellate  connective-tissue  cells, 
whose  branches  form  a  network.  These  cells  float  in 
a  thin  lymph-space,  which  in  part  surrounds  the  ves- 
sel, and  the  two  together  constitute  a  delicate  outer 
or  adventitious  coat  (tunica  advenlitia).  In  some  loca- 
tions the  capillaries  are  completely  invested  by  a  cylin- 
drical lymph-channel,  in  which  case  the  walls  of  the 
channel  are  lined  with  endothelium,  and  the  exterior 
surfaces  of  the  capillaries  are  also  covered  by  similar 
cells.  This  is  usually  the  character  of  the  capillaries 
of  the  brain  and  spinal  cord. 

When  capillaries  run  through  reticular  tissue  their 
walls  are  connected  with  the  branches  of  the  reticu- 
lum  (fig.  6,  Plate  VI.). 

The  capillaries  vary  greatly  in  size  in  different 
locations.  In  the  cerebro-spinal  nervous  system  and 
in  the  lungs  they  are  smallest,  in  the  marrow  of  bone 
they  are  largest. 

Moreover,  in  some  locations,  they  are  quite  irregu- 
lar in  calibre.  In  the  inner  layer  of  the  dura  mater, 
and  in  the  interstitial  connective-tissue  of  many  mus- 
cles, they  sometimes  present  varicosities  or  even 
diverticula  of  odd  forms. 

Many  authors  have  claimed  for  the  capillaries  a 
moderate  contractile  power,  through  the  agency  of 
which  their  calibre  may  be  more  or  less  modified. 

Arteries. — The  simplest  structure  of  the  artery  is 
found  in  the  smallest  vessels  of  this  class.  Such  ves- 
sels are  known  as  arterioles.  The  capillaries  pass  so 
gradually  into  the  arterioles  that  it  is  often  difficult  to 
say  exactly  where  the  one  begins  and  the  other  ends. 
Tue  wall  of  each  arteriole  has  a  much  greater  thick- 
ness than  that  of  the  capillary  in  which  it  ends,  and 
is  more  complex  in  its  structure.  Next  to  the  blood- 
stream lies  the  same  endothelial  layer  as  is  found  in 
the  capillaries.  It  has  also  an  adventitious  coat  ex- 
ternally, which  is  a  further  development  of  the  deli- 
cate tunica  adventitia  surrounding  many  capillaries. 
Between  these  two  inner  and  outer  coats  of  the  arte- 
riole is  a  third  or  middle  muscular  coat.  The  dis- 
tinctive feature  of  the  arteriole  is  the  existence  of 
this  muscular  tissue  in  the  middle  coat  of  the  vessel. 
The  muscle-fibres  are  short,  smooth,  and  spindle-form, 
and  run  around  the  inner  coat  in  a  transverse  direc- 
tion. 

In  that  part  of  the  arteriole  nearest  the  capillary, 
these  transversely  arranged  smooth  muscle-fibres  do 
not  form  a  continuous  layer.  The  cells  are  usually 
a  little  too  short  to  completely  encircle  the  vessel. 
At  intervals,  two  or  three  are  grouped  together  on 


one  side  of  the  arteriole,  while  the  opposite  side 
remains  uncovered.  By  means  of  an  alternation  of 
these  groups  of  cells  around  opposite  sides  of  the 
vessel,  the  arteriole  is  practically  supplied  with  the 
means  of  narrowing  and  widening  its  lumen.  A 
little  nearer  the  heart  the  layer  of  muscle-fibres 

Fig.  40. 


CEREBRAL  ARTERIOLES  (HUMAN). — 1.  Smallest  artery.  2.  Transition  vessel. 
3.  Coarser  capillaries.  4.  Finer  capillaries,  tt.  Structureless  membrane  still 
with  some  nuclei,  representative  of  the  adventitious  coat.  6.  Nuclei  of  the 
muscle-fibre-cells,  c.  Nuclei  within  the  small  artery,  perhaps  appertaining 
to  the  eudothelium.  '/.  Nuclei  in  the  transition  vessels.  Highly  magnified. 
(dray.) 

forms  a  continuous  uninterrupted  membrane.  The 
wall  of  the  smallest  artery  may  then  be  regarded  as 
composed  of  three  coats  or  tunics — the  external  coat 
or  tunica  adventitia,  the  middle  (muscular)  coat  or 
tunica  media,  and  the  inner  coat  or  tunica  intima. 
The  tunica  adventitia  of  the  larger  arterioles  still 
represents  the  tunica  adventitia  or  lymph-sheath  of 
the  capillaries  above  described.  There  is  a  network  of 
branched  corpuscles  which  lie  in  lymph-spaces  formed 
by  a  loose  reticulum  and  felt-work  of  white  fibrous 
tissue.  Between  the  tunica  adventitia  and  the  tunica 
media  in  the  larger  vessels  of  this  class  there  are  fre- 
quently found  a  few  fine  elastic  fibres  collected  into 
a  network.  Between  the  tunica  media  and  the  tunica 
intima  in  these  vessels  is  also  a  small  number  of  elas- 
tic fibres,  the  elastic  layer  of  the  tunica  intima.  Be- 
tween such  a  delicate  elastic  layer  and  the  endothelia 
lining  the  tunica  intima  exist,  even  in  arteries  of  this 
size,  a  small  number  of  branched  connective-tissue 
cells  connected  together  into  a  membranous  network. 
In  arteries  of  a  larger  calibre,  the  various  elements 


BLOODVESSELS. 


71 


entering  into  the  construction  of  the  different  arterial 
tunics  are  more  fully  developed,  while  a  few  other 
characteristics  are  added.  The  tunica  adventitia  has 
gained  in  thickness  by  a  more  complete  development 
of  a  connective  felt- work,  whose  fibres  now  have  a 
prevalent  longitudinal  course.  Scattered  among  these 
bundles  of  white  fibrous  tissue  appear  a  few  fine  elastic 
fibres.  In  the  loose  meshes  formed  by  the  inter- 
crossing of  the  fibrous  bundles  are  more  or  less 
numerous  connective-tissue  corpuscles  and  lymphoid 
cells.  These  loose  meshes  thus  formed  are  lyrnph- 
spaces,  which  very  freely  intercommunicate. 

The  elastic  fibres  become  more  abundant  and  larger 
as  the  tunica  media  is  approached.  At  the  line  of 
union  between  the  outer  and  middle  coats,  the  elastic 
fibres  form  a  dense  network,  and  spread  out  more  or 
less  into  a  fenestrated  membrane  which  constitutes 
the  line  of  division  between  these  two  tunics.  This 
dense  collection  of  elastic  fibres  has  been  termed  the 
external  elastic  membrane. 

The  tunica  media  is  now  constituted  by  'a  much 
more  numerous  collection  of  smooth  muscle-fibres; 
but,  instead  of  forming  as  before  a  continuous  mus- 
cular membrane  composed  of  a  single  layer  of  cells, 
the  latter  are  arranged  in  several  more  or  less  con- 
tinuous layers,  the  cells  of  each  layer,  however,  still 
running  transversely  around  the  axis  of  the  vessel. 
The  several  muscular  layers  of  which  the  tunica 
media  is  now  composed  are  separated  from  each 
other  by  plates  of  elastic  tissue  in  the  form  of  fenes- 
trated membranes.  These  elastic  plates  run  mainly 
longitudinally  and  at  the  same  time  parallel  to  the 
curved  surface  of  the  vessel.  They  are  connected  j 
with  those  internal  and  external  to  them  by  means  ; 
of  networks  of  fine  elastic  fibres  (fig.  3,  Plate  III.) 
which  run  among  the  cells  of  the  muscle-layers.  Be- 
tween the  muscular  membranes  which  the  last-named 
cells  constitute,  is  also  to  be  found  now  for  the  first 
time  a  very  small  amount  of  fibrous  connective-tissue 
with  elements  which  usually  accompany  it. 

At  the  external  boundary  of  the  tunica  intima,  and 
forming  a  sharp,  distinct  line  of  division  between  it  ; 
and  the  media  tunica,  is  another  dense  accumulation  j 
of  elastic  tissue — called  the  internal  elastic  membrane. 
It  consists,  in  small  arteries,  of  two  or  more  fenestrated 
elastic  layers  so  closely  packed  against  each  other  as 
to  present  in  section  an  appearance  of  a  simple  struc- 
tureless elastic  membrane.  Internal  to  this  elastic 
layer  of  the  tunica  intima  is  a  slight  accumulation  of 
delicate  white  fibrous  tissue.  The  direction  of  these 
fibres  is  mainly  longitudinal.  They  intercross,  how- 
ever, at  acute  angles,  and  form  between  them  lymph- 


spaces  elongated  with  the  axis  of  the  vessel.  These 
spaces  contain  fusiform  and  branched  connective-tissue 
corpuscles,  as  well  as  an  occasional  lyrnphoid  cell. 
This  connective  layer  is  covered  internally  by  the 
endothelia  lining  the  lumen  of  the  vessel.  The  out- 
line of  these  cell  plates  is  that  of  a  sharp-pointed 
lozenge,  and  their  edges  are  somewhat  sinuous.  When 
the  artery  is  cut  transversely,  the  internal  elastic 
layer  of  the  tunica  intima  is  shown  beautifully  fes- 
tooned— an  appearance  which  gives  the  inner  surface 
of  the  arterial  wall  an  extremely  wavy  outline.  Seen 
in  face,  the  inner  surface  of  the  artery  appears  cov- 
ered with  longitudinal  folds  or  ridges. 

In  the  large  arterial  trunks,  the  tunica  media  and 
intima  become  much  thicker.  In  the  tunica  media, 
the  number  of  muscular  layers  is  much  increased,  as 
well  as  are  the  thickness  and  size  of  the  elastic  plates 
between  them.  The  elastic  fibres  which  form  a  net- 
work among  the  muscle-cells  are  also  much  stouter 
than  before.  Instead  of  nearly  all  the  muscle-fibres 
running  transversely,  as  in  the  smaller  vessels,  there 
are  to  be  found  in  some  arteries  longitudinal  and  ob- 
lique bundles,  especially  in  the  inner  portion  of  the 
tunica  media.  These  are  occasionally  met  with  in  the 
tunica  adventitia,  but  rarely  in  the  longitudinal  fibrous 
layer  of  the  tunica  intima. 

The  elastic  layer  of  the  tunica  intima  is  much 
thicker,  and  is  also  laminated.  Between  the  laminae 
is  to  be  found  a  small  amount  of  connective-tissue. 
The  layer  of  longitudinal  fibrous  bundles  beneath  the 
endothelial  lining  of  the  lumen  of  the  vessel  is  now 
quite  distinct. 

As  a  rule,  the  larger  the  artery  the  thicker  becomes 
the  muscular  tunic  and  the  more  numerous  the  muscle- 
fibres.  In  the  aorta,  however,  we  have  a  partial 
exception  to  this  rule  (fig.  1,  Plate  VII.).  Of  this 
great  vessel  the  following  characteristics  may  be 
enumerated.  The  tunica  adventitia  is  here  compara- 
tively thin.  The  tunica  media  is  thick,  but  the  lavers 
of  muscular  tissue  are  thin,  and  the  muscle-fibres 
which  constitute  them  are  scattering.  In  the  inner 
portion  of  the  tunica  media  the  elastic  plates  which 
separate  the  muscular  layers  are  also  thickened  and 
laminated.  The  fibres  of  the  elastic  network  which 
unite  the  plates  and  which  anastomose  among  the 
muscle-fibres  are  thick,  tough,  elastic  cylinders,  whose 
main  direction  is  longitudinal  to  the  axis  of  the  vessel. 
In  the  outer  portion  of  the  tunica  media  the  elastic 
plates  are  less  laminated  and  are  not  so  thick  as  in 
smaller  arteries;  neither  are  the  elastic  fibres  so  large. 
An  appreciable  amount  of  connective-tissue  is  scat- 
tered through  the  middle  coat.  The  tunica  intima  is 


72 


HISTOLOGY. 


thicker,  but  does  not  otherwise  differ  from  that  of 
other  large  arteries. 

The  muscle-fibres  of  the  arteries  are  in  the  main 
simple,  smooth,  fusiform  cells  with  rod-shaped 
nuclei.  In  the  larger  trunks  the  ends  may  be  more 
or  less  bifurcated  or  even  branched.  In  the  aorta, 
flattened,  stellate  muscle-cells  are  often  met  with. 

The  walls  of  the  arteries  are  relatively  thick,  and, 
owing  to  the  large  amount  of  elastic  tissue  compos- 
ing them,  the  lumen  is  usually  patulous.  The  thick- 
ness of  the  arterial  wall  varies  considerably,  according 
to  whether  the  vessel  is  distended  or  not.  In  the  large 
vessels  the  outer  and  middle  coats  are  supplied  with 
bloodvessels — the  vasa  vasorum.  In  a  few  instances, 
capillary  vessels  even  enter  the  tunica  intima. 

Veins. — The  veius  differ  considerably  from  the 
arteries.  In  the  first  place,  the  lumen  of  the  vein 
is  usually  considerably  larger  than  in  the  artery  of 
the  same  grade,  yet  the  wall  of  the  vein  is  much  the 
thinner.  There  are  differences  also  in  the  minute 
structure.  The  smallest  vessels  which  collect  the  blood 
from  the  capillaries  are  known  as  venules.  Their 
walls  are  extremely  thin,  yet  they  can  be  readily 
differentiated,  as  with  the  arteries,  into  three  coats — 
the  external  or  tunica  adventitia,  the  middle  or  tunica 
m.edia,  and  the  internal  or  tunica  intima.  The  tunica 
adventitia  consists  of  a  simple  network,  of  fusiform  or 
stellate  cells  floating  in  a  narrow  lymph-channel.  The 
tunica  media  is  composed  of  simple  connective-tissue 


scarcely  differentiated.  It  contains  as  yet  no  muscle- 
elements.  The  tunica  intima  is  very  thin,  and  is 
separated  into  thin  layers  which  closely  correspond 
to  those  of  the  tunica  intima  of  arterioles.  The 
outer  layer  consists  of  a  delicate  fibrous  membrane 
with  the  fibres  running  longitudinally.  The  middle 
layer  is  represented  by  a  few  stellate  cells  with  their 
branches  anastomosing.  Resting  upon  these  stel- 
late cells  is  the  inner  layer  composed  of  thin  endo- 
thelial  cell-plates  similar  to  those  of  the  arteries  in 
all  except  outline.  They  are  much  broader  and 
shorter  than  are  the  same  cells  of  the  arteries,  and 
have  rather  more  sinuous  outlines.  Sti/jmata  and 
ttomata  are  formed  here  as  in  the  capillaries,  and  there 
may  be  consequently  out-wandering  of  the  blood-cells. 
In  veins  of  a  little  larger  calibre,  the  tunica  adven- 
titia increases  in  thickness  and  strength  by  an  acces- 
sion of  fibrous  bundles,  which  have  a  prevalent 
longitudinal  direction,  but  which  branch  and  inter- 
lace in  such  manner  as  to  form  a  loose  meshwork  in 
which  lie  branched  connective-tissue  corpuscles,  and 
a  few  lymphoid  elements.  At  the  junction  of  the 
tunica  adventitia  with  the  tunica  media  the  connec- 
tive-tissue bundles  are  aggregated  so  as  to  form  a 
more  or  less  distinct  fibrous  membrane,  corresponding 
in  position  to  the  external  elastic  membrane  of  the 
arteries.  In  most  veins  of  this  size  the  tunica  media 
contains,  in  addition  to  the  elements  of  loose  connec- 
tive-tissue, a  few  scattered,  smooth  muscle-fibres  ar- 


EXPLANATION  OF  PLATE  VII. 


Fig.   1.    Longitudinal   section   of  thoracic   aorta  of  Man. 

High  power.     (After  Ranvier.) 
The  central  part  of  the  middle  coat  is  not  drawn. 

1.  Internal  layer  of  the  internal  coat,  or  tunica  intima. 

2.  External  layer  of  the  internal  coat. 

3.  Elastic  lamina  dividing  the  internal  and  middle  tunics 
of  the  artery. 

4.  5.    Smooth  muscular   fibres  of  the  middle  coat,  cut 
transversely  ;  among  them  are  elastic  fibres  and  elastic  plates. 

6.  External  coat. 

Fig.  2.    Showing  development  of  capillary  bloodvessels  in 
the  normal  omentum  of  a  Rabbit.     High  power.    (After 
Klein.) 
a,  Capillary  bloodvessels  ;  5,  connection  of  the  capillaries 

witli  branched  cells  of  the  extravascular  tissue.      It  is  by 

metamorphosis  of  these  branched  cells  that  new  vessels  are 

formed. 


Fi":  3.   Shows  an  artificial  injection  of  the  blood  and  lymph- 
vessels  of  the  parietal  peritoneum.     Medium  enlarge- 
ment. 
I,  Network  of  lymph-trunks  ;  v,  venules  and  arterioles  ; 

c,  capillary  bloodvessels. 

Fig.  4.  A.  Shows,  under  a  moderate  power,  an  injection 
of  the  capillary  network  in  the  walls  of  the  alveoli  of  au 
inflated  lung.  The  vessels  were  filled  from  the  pulmonary 
artery. 

B.  An  injection  of  the  pulmonary  blood-capillaries  (I)  in 
the  lung  of  a  human  foetus — the  air-vesicles  (a)  never  having 
been  inflated. 

Fig.  5.    Shows  a  silver  injection  of  the  bloodvessels  of  the 

lung  of  a  Frog.     High  power. 

v,  Larger  vessel ;  v',  small  arteriole  which  distributes  its 
blood  to  capillaries  (c)  in  the  walls  of  the  air- vesicles ;  a, 
inter-capillary  areas. 


p  L  A  T  £     V  ; ! 


FigT 


BLOODVESSELS. 


73 


ranged  transversely.  The  tunica  intima  is  extremely 
thin,  and  presents  the  same  structure  as  in  the 
venules. 

In  the  larger  venous  trunks  the  structure  of  the 
vessel  is  essentially  the  same  as  that  of  the  vessels 
last  described.  The  tunica  adventitia  is  strengthened 
by  the  presence  of  a  greater  quantity  of  connective- 
tissue  fibres.  The  tunica  media  in  most  cases  contains 
a  number  of  muscle-layers  with  the  cells,  for  the  most 
part  running  transversely ;  elastic  tissue  is,  however, 
entirely  absent.  The  layers  of  muscle-cells  are  sepa- 
rated by  lamellas  of  fibrous  tissue  whose  individual 
bundles  pursue  a  general  longitudinal  course.  The 
outer  layer  of  the  tunica  intima  consists  of  a  dense 
fibrous  membrane,  sometimes  laminated.  The  sub- 
endothelial  layer  contains  longitudinal  fibrous  bun- 
dles, in  the  interspaces  of  which  are  stellate  and 
lymphoid  cells.  The  endothelial  lining  is  not  dif- 
ferent from  that  of  the  smaller  veins. 

In  many  veins,  the  tunica  media  possesses  no  mus- 
cle-fibres. The  veins  of  bone,  of  muscle,  of  the  retina, 
of  the  membranes  of  the  brain  and  spinal  cord,  the 
cardiac  ends  of  venous  trunks  emptying  into  the 
superior  vena  cava  have  no  muscles.  Some  veins 
possess  only  a  longitudinal  muscular  coat,  as  the  veins 
of  the  pregnant  uterus.  Others  possess  an  outer  lon- 
gitudinal and  inner  circular  layer  of  muscle-fibres. 

In  some  veins,  the  distribution  of  the  muscle-fibres 
is  not  limited  to  the  middle  coat.  They  are  not  infre- 
quently found  in  the  tunica  adventitia,  and  are  occa- 
sionally present  even  in  the  tunica  intima. 

The  foregoing  division  of  the  walls  of  veins  into 
three  distinct  coats  as  in  the  arteries  is  not  accepted 
by  all  investigators.  Eanvier  thinks  that  the  walls 
of  these  vessels  should  be  regarded  as  consisting  of  ' 
only  two  tunics,  an  inner  and  an  outer.  According 
to  him,  it  is  in  the  innermost  portion  of  the  latter 
that  muscle-fibres  are  usually  located,  but  they  may 
at  times  be  found  throughout  the  greater  part  of  its 
thickness. 

Nearly  all  the  veins  are  furnished  with  valves  for 
the  purpose  of  preventing  a  backward  flow  of  the 
'blood.  At  the  location  of  the  valves,  there  is  a  slight 
ampullar  enlargement  of  the  calibre  of  the  vein,  a 
provision  which  prevents  a  serious  encroachment  upon 
the  diameter  of  the  blood-channel  when  the  valves  I 
are  open  and  their  leaflets  flattened  against  the  walls  of 
the  vessel.  The  following  peculiarities  in  the  structure 
of  the  valves  maybe  adverted  to  here:  Each  surface 
is  covered  with  a  single  layer  of  endothelial  plates. 
Upon  the  inner  surface  the  endothelia  are  entirely 
similar  to  those  lining  the  vein,  i.  e.,  more  or  less 
10 


lozenge-shaped,  with  the  long  axis  parallel  to  the 
axis  of  the  vein.  Upon  the  outer  surface,  however, 
the  long  axis  of  the  endothelial  plates  is,  in  the  main, 
transverse  to  the  axis  of  the  bloodvessel.  Imme- 
diately beneath  the  endothelium  is  a  subendothelial 
layer  of  connective-tissue  fibres  interspersed  with  a 
few  elastic  fibres.  This  layer  is  thicker  and  much 
more  abundant  in  elastic  fibres  upon  the  inner  than 
upon  the  outer  surface  of  the  valve.  Between  and 
upon  these  fibres  connective-tissue  cells,  both  fixed 
and  wandering,  are  present  in  variable  number.  The 
subendothelial  layers  of  the  two  surfaces  of  the  valve 
are  separated  from  each  other  by  a  thin,  tough,  fibrous 
membrane  composed  of  interlacing  white  fibrous 
bundles  whose  general  direction  is  parallel  to  the 
edge  of  the  valve.  Some  elastic  fibres  are  also  scat- 
tered among  the  white  fibrous  bundles,  and  according 
to  the  statements  of  some  authors  a  few  muscle-fibres 
may  be  found  near  the  base  of  the  valve.  When 
muscle-fibres  are  present,  the  direction  of  their  long 
axis  is  usually  transverse  to  the  axis  of  the  vessel. 
The  endothelium  and  the  subendothelial  layer,  lining 
the  ampullar  enlargement  of  the  vein  at  the  location 
of  the  valves,  are  similar  to  those  which  cover  the 
outer  surface  of  leaflets  of  the  valve. 

Sinuses. — Custom  among  anatomists  has  fixed  upon 
the  term  sinus  a  double  and  somewhat  indefinite  sig- 
nificance. Many  vessels  of  the  human  economy  which 
have  received  this  name  possess  no  circumstance 
which  distinguishes  them  from  veins,  other  than  the 
simple  fact  that  they  constitute  various  channels  in 
fibrous  membranes,  e.  </.,  some  of  the  cerebral  sinuses. 
Most,  if  not  indeed  all,  of  the  sinuses  of  the  blood- 
vascular  system  may  be  justly  regarded  as  varieties 
of  veins,  for  their  blood  is  that  of  the  venous  system, 
and  so  also  in  many  respects  is  their  histology. 

The  cavernous  sinus,  and  the  cavernous  tissue  of 
the  corpus  cavernosum  of  the  penis,  present  two  dis- 
tinct types  of  genuine  sinuses. 

In  the  former  we  have  a  vein  whose  calibre  is 
broken  up  into  reticulas  of  various  sizes  and  shapes 
by  fibrous  trabeculae  springing  from  the  walls  of  the 
sinus,  and  extending  across  the  lurnen  of  the  vessel. 
The  fibrous  bundles  are  continuous  with  the  middle 
tunic  of  the  vessel,  and  contain  such  elements  as  are 
present  in  that  coat.  The  trabeculae  are  covered  by 
endothelial-cells  and  a  subendothelial  tissue  similar 
to  those  of  the  walls  of  the  sinus.  They  sometimes 
inclose  small  bloodvessels. 

The  corpus  cavernosum  of  the  penis  presents  a 
somewhat  different  construction.  As  its  name  im- 
plies, it  is  a  cavernous  tissue.  It  consists  essentially 


HISTOLOGY. 


of  a  reticulurn  of  interlacing  bands,  or  trabeculae  of 
smooth  muscle-fibres,  associated  with  a  variable 
amount  of  elastic  fibres  and  bundles  of  white  fibrous 
tissue.  The  spaces  formed  by  the  interlacement  of 
these  trabeculae  are  of  variable  size  and  outline,  and 
they  freely  intercommunicate.  The  surfaces  of  the 
trabeculae  are  covered  with  a  layer  of  endothelial 
cells  and  a  subendothelial  tissue  very  similar  to  those 
of  large  veins.  The  trabeculae  contain  arterioles 
which  distribute  their  blood  to  a  plexus  of  capillary 
vessels  which  also  are  contained  within  the  trabeculas. 
Most  of  these  capillaries  empty  into  the  cavernae 
formed  by  the  interlacing  trabeculae.  The  blood  of 
these  sinuses  or  caverna3  is  collected  by  venous  trunks, 
and  the  communicating  cavernae  may  consequently  be 
regarded  as  a  complicated  venous  sinus. 

Development  of  bloodvessels. — The  earliest  form  of 
the  complete  bloodvessel  is  the  capillary.  By  the 
successive  addition  of  the  elements  which  constitute 
their  distinctive  features,  arteries  and  veins  are  formed 
from  vessels  which  were  originally  in  the  condition 
of  capillaries.  These  minute  blood-channels  fre- 
quently give  origin  to  new  capillaries  in  the  following 
manner : — 

In  young,  growing  connective- tissue  the  walls  of 
the  simplest  form  of  capillary,  above  described,  here 
and  there  give  off  solid  protoplasmic  projections, 
which  may  be  more  or  less  branched,  and  which  are 


frequently  irregular  in  outline  (fig.  2,  Plate  VII.). 
The  nuclei  contained  in  these  solid  protoplasmic 
cylinders  divide  and  increase  in  number.  The  por- 
tion in  connection  with  the  previously-formed  capil- 
lary becomes  hollowed  out  and  filled  with  blood 
from  the  open  lumen  of  the  vessel.  In  the  portion 
more  remote  from  the  capillary,  vacuoles  appear  at 
intervals  in  the  protoplasmic  cylinder.  These  soon 
open  into  one  another,  and  constitute  a  channel  in  the 
protoplasmic  branch.  By  an  extension  of  this  pro- 
cess of  vacuolation  a  hollow  tube  is  produced,  the 
lumen  of  which  freely  communicates  with  the  lumen 
of  the  original  capillary.  As  this  process  of  vacuola- 
tion proceeds,  the  nuclei  are  pushed  to  the  side  of  the 
protoplasmic  cylinder,  where  they  remain  to  form  the 
nuclei  of  the  future  endotheliurn.  The  calibre  of  the 
new  capillary  ultimately  becomes  regular  in  outline, 
and  what  remains  of  the  original  protoplasm  of  the 
tube  divides  into  endothelial  plates  and  their  intercel- 
lular cement. 

Instead  of  the  formation  of  a  new  capillary  loop 
by  vacuolation  of  a  protoplasmic  projection  from  the 
wall  of  a  capillary,  a  connective-tissue  corpuscle, 
which  by  one  of  its  branches  is  connected  with  the 
wall  of  a  capillary,  may  swell  up,  experience  division 
of  its  nucleus,  enlargement  of  its  branches,  and  through 
the  same  process  of  vacuolation  be  converted  into  a 
young  capillary. 

This  process  of  vacuolation  may  even  affect  eon- 


EXPLANATION  OF  PLATE  VIII. 


Fig.  1.  An  injection  of  the  bloodvessels  of  a  racemose  gland, 
as  seen  in  a  very  thin  section.  Medium  enlargement. 

Fig.  2.  Scheme  of  the  relations  and  distribution  of  the 
bloodvessels  of  the  kidney.  Low  power.  (After  Lud- 
wig.) 

A.  External  portion  of  the  cortex  ;  c  being  the  limiting 
capsule.  B.  The  cortex.  C.  Boundary  layer.  D.  The 
medulla.  E.  The  apex  of  the  papilla. 

a,  Portion  of  a  small  artery  coursing  along  the  boundary 
between  the  cortex  and  medulla, — it  gives  off  an  external 
twig  (inter-lobular  branch),  which  at  varying  intervals  dis- 
tributes an  afferent  arteriole  to  a  Malpighian  glomerulus,  m  ; 
V,  corresponding  vein  which  receives  an  analogous  external 
(inter-lobular)  branch, — the  latter  collects  blood  directly  from 
the  efferent  vessels  of  the  glomeruli,  JM,  and  from  (r)  the 
capillary  network  (rete  mirabile)  surrounding  the  tortuous 
nriniferous  tubes  of  the  renal  cortex,  and  it  drains  the  renal 
medulla  directly  through  bundles  of  venulce  rectce,  which 


empty  into  the  inter-lobular  vein  as  represented  at  v,  on  the 
left  of  the  figure.  Corresponding  to  the  venuloe  recta;  are 
the  arteriolce  recta,  not  represented  in  the  diagram,  which 
arise  at  the  base  of  the  inter-lobular  arterial  twigs. 

• 

Fig.  3.   Arrangement  of  bloodvessels  in  an  intestinal  villus. 

High  power, 
a,  Arteriole  ;  v,  collecting  venule ;  c,  capillary  plexus. 

Fig.  4.   Arrangement  of  bloodvessels  in  a  filiform  papilla  of 

the  tongue.     High  power. 
a,  Arterioles  ;  v,  collecting  venules  ;  I,  capillary  loops. 

Fig.  5.  Arrangement  of  minute  bloodvessels  in  the  muscular 

tissue  of  the  tongue.     Medium  enlargement, 
a,  Arteriole ;  m,  capillary  plexus,  the  long  axis  of  whose 
meshes  corresponds  with  the  length  of  the  muscular  fibre ; 
t,  capillaries  running  with  muscle-bundles,  which  are  vertical 
to  the  surface  of  the  section. 


PLATE    VIII 


A 


Fig.  4. 


NERVOUS    TISSUE. 


75 


nective-tissue  corpuscles  at  some  distance  from  a 
capillary  and  not  in  direct  communication  with  it,  and 
thereby  influence  the  formation  of  hollow  protoplasmic 
tubes,  which  finally  form  a  connection  with  the  capil- 
laries. 

Those  connective- tissue  corpuscles  which  take  part 
in  the  formation  of  new  vessels,  Eanvier  regards  as 
cells  of  special  function,  namely,  the  formation  of 
vessels.  He  has  called  them  vasoformative  celk. 

Fig.  41. 


VARIOUS  FORMS  OF  MOTHER-CELLS  (SO-CALLED  VASOFORMATIVE  CELLS)  tINDER- 
OOI.NU    DEVELOPMENT    INTO    BLOODVESSELS,   FROM    THE    MIDDLE    LAYER    OF  THB 

CHICK'S  BLASTODERM  (KLEIN). — a.  Large  mother-cells  vacnolated,  forming  the 
ruilinieuts  of  vessels,  b.  Their  walls,  formed  of  protoplasm,  with  nuclei  em- 
bedded and  in  some  cases  more  or  less  detached  and  projecting,  d.  Blood-cor- 
puscles. /.  Small  mother-cells— vacuolation  commencing.  B.  Mother-cell  in 
which  only  obscure  granular  matter  is  found. 


In  the  development  of  new  capillary  bloodvessels 
from  connective-tissue  corpuscles,  the  elements  of  the 
blood  are  sometimes  formed  in  small  numbers,  by  a 
process  similar  to  that  of  the  original  formation  of 
blood  and  bloodvessels  in  the  embryo.  They  may 
more  or  less  completely  fill  the  channels  of  the  vaso- 
formative cells,  even  before  a  communication  is  effected 
with  the  lumen  of  a  previously-formed  capillary. 

The  method  of  formation  of  the  earliest  bloodves- 
sels in  the  embryo  is  essentially  identical  with  that 
by  which  a  so-called  vaso-formative  cell  of  the  young 
or  adult  animal  is  transformed  into  a  capillary.  The 
bloodvessels  are  thus  derived  from  the  middle  layer 
of  the  blastoderm. 

Arrangement  of  the  bloodvessels. — By  branching  the 
arteries  diminish  in  calibre  until  the  arteriole  is 
reached.  These,  after  running  a  short  distance,  almost 
always  pass  into  a  capillary  network,  which  in  its 
turn  yields  its  blood  to  a  collecting  venule.  In  a 
few  instances,  however,  the  arterioles  discharge  their 
blood  into  the  veins  without  the  intermediation  of 
capillary  vessels.  This  is  the  case,  for  example,  in  the 
matrix  of  the  nails,  and  in  the  ends  of  the  fingers  and 
toes.  In  the  cavernous  tissue  of  the  genital  organs 


a  similar  direct  communication  between  the  arteries 
and  veins  exists.  Like  the  arteries,  the  veins  also 
vary  their  diameter  as  branches  are  received.  This 
is  not  so,  however,  with  the  capillaries,  whose  calibre 
is  neither  increased  nor  lessened  by  ramifying.  The 
branch  is  usually  of  the  same  size  as  the  capillary 
from  which  it  receives  its  blood  and  the  one  into 
which  it  empties. 

The  distribution  of  the  terminal  bloodvessels  varies 
according  to  the  arrangement  of  the  elements  of  the 
tissues  in  which  they  ramify.  (Refer  to  descriptive 
text  accompanying  Plate  VIII.) 


NERVOUS  TISSUE. 

The  nervous  system  comprises  nerve-centres,  pe- 
ripheral terminations,  conducting  fibres  uniting  them, 
conimissural  fibres  running  from  centre  to  centre,  and 
a  connective-tissue  framework. 

The  whole  nervous  apparatus  has  generally  been 
considered  under  two  divisions,  the  cerebro-spinal 
system  and  the  sympathetic  system. 

In  the  cerebro-spinal  system  we  have  nerve-centres 
constituted  by  nerve  ganglia,  or  yray  substance,  and 
conducting  fibres,  or  white  substance.  From  these 
centres  nerves  pass  to  various  parts  of  the  economy. 

CEBEBRO-SPINAT;  NERVES. 

Nerve-sheath. — Cerebro-spinal  nerves,  after  leaving 
their  centres,  are  surrounded  by  a  sheath  of  white 
fibrous  connective-tissue,  in  which  there  is  a  certain 
amount  of  yellow  elastic  tissue. 

At  the  exterior  this  fibrous  tissue  is  somewhat 
denser  than  ordinary  loose  connective-tissue,  and  pre- 
sents characters  very  similar  to  those  of  the  cutis. 
Within  this  denser  envelope  the  fibrous  bundles  and 
other  elements  are  arranged  in  a  manner  analogous 
to  the  loose  connective-tissues  elsewhere. 

The  arteries  and  veins  of  the  nerve-trunk  ramify 
in  this  loose  tissue,  and  the  lymph  also  courses 
through  it.  As  in  other  loose  connective-tissue,  adi- 
pose vesicles  may  be  found  between  the  fibres.  This 
fibrous  tissue  is  technically  known  as  the  epineurium 
— a  continuation  of  the  dura  mata.  A  cerebro-spinal 
nerve  contains,  within  the  epineurium,  one  or  more 
bundles  of  individual  nerve  -  fibres.  Immediately 
around  the  bundle  of  the  nerve-fibres  the  connective- 
tissue  of  the  epineurium  becomes  condensed  into  a 
laminated  enveloping  membrane — the  perineurinm — 
a  continuation  of  the  arachnoid.  Between  the  lam- 


76 


HISTOLOGY. 


inae  of  the  perineurium  exist  shallow  lymph-spaces, 
containing  connective-tissue  elements,  and  partially 
lined  by  endothelium.  The  perineurium  may  inclose 
a  single  bundle  (funiculus)  of  individual  nerve-fibres, 
or  it  may  ensheathe  a  number  of  such  bundles,  and 
constitute  what  has  been  termed  a  nerve-fasciculus. 

Neuro'jlia.  —  In  the  simple  funiculus  the  nerve- 
fibres  are  more  or  less  closely  packed  side  by  side, 
imbedded  in  a  soft,  semifluid,  somewhat  granular 
substance,  in  which  are  scattered  a  few  very  fine 
connective-tissue  bundles,  a  number  of  minute  indi- 
vidual fibrillaa,  and  some  flat  and  branched  connective- 
tissue  corpuscles.  In  this  tissue  (the  endoneurium — 
a  continuation  of  the  neuroglia),  run  the  capillary 
vessels,  with  much  elongated  meshes.  As  the  endo- 
neurium approaches  the  periucuriurn,  it  often  becomes 
condensed  into  a  more  resistant  layer,  which  is  slightly 
separated  from  the  inner  lamina  of  the  perineurium  by 
a  thin  encircling  lymph  space  (a  continuation  of  the 
subarachnoid  space).  At  very  numerous  points  this 
lymph-space  is  crossed  by  uniting  trabeculae  of  con- 
nective-tissue, and  is  everywhere  lined  by  a  layer  of 
endothelia.  When  the  perineurium  ensheathes  a 
number  of  funiculi,  the  latter  are  separated  from  each 
other  by  more  or  less  complete  partitions  of  the  en- 
doneurium, consisting  of  fibrous  septa  from  the  inner 
surface  of  the  perineurium. 

The  fine  connective  fibrillae  of  the  endoneurium 
between  the  nerve-fibres  are  often  closely  interlaced 
around  the  nerve-cylinders  as  if  to  constitute  for  the 
latter  a  special  protection.  The  endoneurium,  besides 
carrying  the  capillary  bloodvessels,  is  permeated  by 
a  network  of  capillary  lymph- spaces. 

Nerve-fibres,  medullated  and  non-medullated. — The 
nerve-fibre,  nerve-cylinder,  or  nerve-tube  will  be  now 
described.  When  an  ordinary  cerebro-spinal  nerve 
is  cut  across  transversely,  after  proper  hardening,  the 
section  offers,  under  a  moderate  power  of  the  micro- 
scope, an  appearance  well  represented  in  fig.  1,  Plate 
IX.  Within  the  perineuria  (c),  which  present  circular 
sections,  are  cross-cuts  of  simple  bundles  or  funiculi  of 
nerve-tubes.  In  the  granular  ground-substance  (the 
endoneurium)  are  a  few  delicate  fibrous  bundles. 
Scattered  more  or  less  unevenly  through  the  endo- 
neurium are  seen  small,  round,  light  spots,  and  in  or 
near  the  centre  (d)  of  each  is  a  dark  dot.  The  latter 
corresponds  to  the  central  or  conducting  fibres  (the 
axis  cylinder)  of  the  nerve-tube,  and  the  light  ring 
around  it  is  an  ensheathing  insulating  cylinder  of 
fatty  material  (the  medullary  sheath).  These  light, 
circular,  dotted  spots  are  sections  of  medullated  nerve- 
fibres.  Each  considerable  bundle  of  nerves  contains, 


besides  the  medullated  tubes,  a  number  c?  non-medul- 
lated nerve-fibres. 

The  fully-developed  medullated  nerve-fibre,  when 
fresh  and  properly  prepared,  presents  the  following 
characteristic  structures:  the  axis-cylinder,  the  me- 
dullary sheath,  and  the  sheath  of  Schwann,  or  neuri- 
lemma  (Figs.  42-46). 

a.  The  axis-cylinder  is  a  finely-fibrillatcd  cord  run- 
ning nearly  in  the  axis  of  the  nerve-tube.  It  consists 
of  a  small  bundle  of  extreme- 
ly fine  unbranched  fibrils,  held 
very  closely  together  by  an 
albuminous  semifluid  cement- 
substance,  which  often  contains 
very  minute  granules  ar- 
ranged in  rows  between  the 
fibrils,  (b,  Fig.  43.) 

Fig.  42. 


Fig.  43. 


DIAGRAM  OF  STurcTCRE  OF  MEDCI.LATED 
NERVE-FIBRE.— 1.  Neurilcmma  or  sheath  of 
Schwann.  2.  Medullary  sheath.  3.  Axis- 
cylinder.  (Carpenter.) 


Fig.  44. 


0, 


1 

O3 


o 


NERVE-TUBES. — a.  Nerve-tube  of  the  com- 
mon European  Eel  in  water.  The  delicate 
line  on  its  exterior  indicates  the  neurilem- 
iti;i.  The  dark  double-edged  inner  line  is 
the  white  substance  of  Schwann,  slightly 
wrinkled  and  divided  into  bevelled  seg- 
ments, b.  The  same  in  ether.  Several  oil 
or  neurine  globules  have  coalesced  in  the 
interior,  and  others  accumulated  around 
the  exterior  of  the  tube.  The  white  sub- 
stance has  in  part  disappeared.  Magnified 
300  diameters.  (Gray.) 


AXIS-CYLINDERS  OF  NEKVES. 
— a.  Axis-cylinder,  showing  its 
fibrillar  structure  ;  at  the  upper 
part,  x,  a:,  it  is  seen  to  arise  from 
a  ganglion-cell,  only  partially 
represented,  and  to  become  in- 
closed by  a  medullary  sheath  at 
a',  b.  Naked  axis-cylinder,  from 
the  dorsal  region  of  the  spinal 
cord  of  the  Ox.  The  medullary 
sheath  has  been  removed.  High 
power.  (Strieker.) 


b.  The  medullary  sheath  enveloping  the  axis-cylinder 
is  not,  asformerly  supposed,  a  continuousuninterrupted 


NERVOUS    TISSUE. 


77 


insulating  tube.  It  is  composed  of  a  great  number  of 
short  tubular  sections,  placed  end  to  end,  or  imbricated. 
The  ends  of  these  sections  are  bevelled  as  represented 
very  poorly  in  a,  Fig.  44.  Each  of  these  bevelled-edged 
tubal  sections  consists  of  a  fatty,  semifluid  substance, 
held  within  the  meshes  of  a  fine  reticulum  (Klein). 
This  fatty  substance  has  long  been  known  as  neurine. 
Water,  pressure,  and  various  reagents  cause  the  semi- 
fluid fat  of  these  sections,  which  normally  is  homo- 
geneous, to  break  up  into  granules  and  drops.  The 
medullary  cylinder  then  becomes  coarsely  granular, 
and  if  the  neurilemma  be  broken  the  fat  extrudes  in 
drops  of  considerable  size,  as  shown  in  b,  Fig.  44. 

Fig.  45. 


HC.MAX  XKRVE-TPBE*,  highly  magnified.  Four  of  them  are  fine,  one  being 
varicose,  and  two  of  middling  thickness  and  of  simple  contour;  whilst  three 
are  thick,  two  of  which  are  double-contoured,  and  one  incloses  grumous  contents. 
(Gray.) 

c.  The  neurilemma,  or  sheath  of  Schwann,  is  a  deli- 
cate, elastic,  homogeneous  membrane,  which  envelops 
the  medullary  cylinder  as  a  continuous  tube.  It  is 
the  analogue  of  the  sarcolemma.  Between  the  neuri- 
lemma and  the  medullary  sheath  is  a  thin  lymph-space. 
The  axis-cylinder  and  the  surrounding  medullary 
sheath  are  also  slightly  separated  by  a  thin  lymph- 
space.  This  latter  lymph-space  is  probably  in  commu- 
nication with  the  outer  lymph-space  beneath  the  neu- 
rilcmrna,  by  means  of  the  spaces  between  the  bevelled 
ends  of  the  tubal  sections  of  the  medullary  cylinder. 
Nodes  of  Ranvier. — The  neurilemmais  not  a  tube  with 
straight  sides,  and  even  calibre  from  one  end  to  the  other, 
but  presents  at  more  or  less  regular  intervals  sharp 
annular  constrictions  (a,  Fig.  46),  which  divide  the 
nerve-tube  into  segments.  At  the  place  of  these 
annular  constrictions,  first  described  by  Ranvier,  a 
septum  from  the  neurilemma  passes  across  the  nerve- 
fibre  interrupting  all  of  its  parts  except  the  axis- 


Fig.  46. 


POO 


cylinder  and  the  lymph-space  immediately  surround- 
ing the  latter.  When  a  perfectly  fresh  and  uninjured 
medullated  nerve-fibre  is  treated 
by  nitrate  of  silver,  and  exposed 
to  light,  the  annular  constriction 
becomes  very  distinct.  If  the 
nerve  is  submitted  long  enough 
to  the  action  of  the  silver  salt,  the 
latter  will  penetrate  to  the  periaxial 
lymph-space  around  the  axis  cylin- 
der, and  extend  along  it  for  a  little 
distance.  When  this  is  the  case 
the  surface  of  the  axis-cylinder  is 
covered  by  transverse  markings 
(lines  of  frommann),  which  are  due 
to  coagulations  in  the  lymph-space. 
In  consequence  of  this  dark  stain- 
ing of  the  annular  constrictions, 
and  of  the  axis- cylinders  for  some 
distance  above  and  below  them,  a 
dark  cross  becomes  conspicuous. 
These  constrictions  are  known  as 
the  nodes  of  Ranvier,  and  the  por- 
tions of  the  nerve- cylinder  between 
the  constrictions  are  known  as 
inter-annular  segments.  Each  in- 
terannular  segment  comprises  a 
number  of  bevelled-edged  imbri- 
cated tubular  sections  of  the  medullary  sheath,  and 
also  contains  a  flattened  nucleated  corpuscle.  The 
nucleus  of  this  cell  consists  of  a  fine  reticulum  and 
an  enveloping  membrane  of  double  contour.  It  is 
a  flattened-oval  in  shape,  and  is  surrounded  by  a 
small  amount  of  protoplasm  which  also  contains  a 
fine  reticulum.  The  corpuscle  is  flattened  upon  and 
partially  sunk  into  the  surface  of  the  medullarysheath, 
sometimes  extending  across  one  or  more  bevelled 
sections  of  the  cylinder.  It  has  no  connection  with 
the  neurilemma.  It  is  the  analogue  of  the  muscle- 
corpuscle,  and  has  been  named  the  nerve-corpuscle. 

Size  of  nerve-fibres. — The  size  of  a  medullated  nerve- 
fibre  varies  according  to  the  diameter  of  the  axis- 
cylinder,  and  the  thickness  of  the  insulating  sheath 
or  medullary  cylinder.  The  thickness  of  the  medul- 
lary sheath  to  some  extent  varies  with  the  distance 
to  which  the  nervous  impulse  is  to  be  conducted. 
The  greater  the  course  the  nerve-fibre  has  to  traverse, 
the  greater  the  thickness  of  the  insulating  cylinder, 
is  a  rule  which  has  numerous  exceptions. 

In  the  nerve-centres  the  medullary  sheath  is  compa- 
ratively thin,  except  in  certain  tracts  of  the  spinal  cord, 
where  fibres  which  run  a  great  distance  are  located. 


NERVE-FICEE  FROM  THE 
SCIATIC  NERVE  OF  THE 
RABBIT  AFTER  THE  AC- 
TION OF  NITRATE  op  SIL- 
VER.— a.  Ring  formed  by 
thickened  membrane  of 
Schwaon.  m.  White  sub- 
stance of  Schwann  ren- 
dered transparent  by  gly- 
cerin. Cy.  Cylinder-axis, 
which  just  above  and  be- 
low the  level  of  the  an- 
ntilar  constriction  pre- 
sents the  lines  of  From- 
mann.  (Frommann.) 


78 


HISTOLOGY. 


As  the  medullary  nerve-fibre  approaches  its  peri- 
pheral termination,  its  medullary  cylinder  gradually 
becomes  thinner  and  thinner  until  it  entirely  disap- 
pears, leaving  only  some  flat  nerve-corpuscles  between 
the  neurilemma  and  the  axis-cylinder.  There  are 
many  nerve-fibres  of  this  structure  to  be  seen  in 
nearly  every  section  of  a  nerve-bundle.  They  are 
generally  scattered  around  unevenly  among  the  fibres 
which  are  still  medullated.  In  a  given  nerve-bundle 
the  medullary  fibres  may  be  nearly  uniform  in  size, 
or  they  may  have  very  different  diameters. 

Division  of  nerve-fibres. — In  their  course  the  nerve- 
bundles  generally  branch  in  order  to  widen  the  ex- 
tent of  their  distribution.  In  some  instances  branches 
derived  from  two  or  more  bundles  are  bound  together 
to  form  a  nerve-bundle.  In  this  manner  a  plexus  of 
nerve-bundles  may  be  formed  within  a  common  epi- 
neurium.  Occasionally,  also,  complete  nerves  may 
branch  and  form  nerve-plexuses. 

While  the  branching  of  whole  nerves  and  of  their 
constituent  bundles  is  of  universal  occurrence,  it  has 
been  doubted  if  the  individual  medullated  fibres  ever 
divide.  Some  well-reputed  authors  have  in  recent 
years  both  described  and  figured  an  occasional  bifur- 
cation of  medullated  nerve-fibres,  especially  when 
near  their  peripheral  termination.  This  bifurcation 
takes  place  invariably  at  one  of  the  nodes  of  Ean- 
vier.  The  axis-cylinder  divides,  and  each  branch  is 
enveloped  in  a  neurilemma  and  medullary  sheath 
which  are  continuations  of  those  which  surround  the 
fibre  above  the  point  of  division. 

Microscopic  nerve-bundle. — In  branching,  a  nerve 
becomes  smaller  and  smaller  and  its  constitution  less 


Fig.  47. 


and  less  complex  until  a  microscopic  size  is  reached. 
This  microscopic  nerve  may  consist  of  a  single  small 
bundle  of  medullated  and  other  fibres  ensheathed  in 
a  perineurium,  which,  instead  of  being  formed  by 
dense  lamellated  connective-tissue,  is  represented  by 
a  delicate  film  of  connective-tissue.  The  external 
surface  of  the  endoneurium,  as  in  the  larger  nerves, 
is  still  covered  by  an  investment  of  endothelia.  The 
appearance  of  such  a  microscopic  nerve,  after  it  has 
been  withdrawn  from  its  perineural  sheath  and  sub- 
mitted to  the  action  of  nitrate 
of  silver  and  light,  is  very  well 
represented  in  Fig.  47. 

A  microscopic  funiculus  of 
this  character  continues  to  di- 
vide and  subdivide  until  the 
smallest  microscopic  med  ullated 
nerve  is  reached,  inclosed  in  a 
perineurium  composed  of  a  sin- 
gle layer  of  endothelial  cells. 

These  smallest  medullated 
nerves  are  not  infrequently 
slightly  moniliform — an  irreg- 
ularity of  outline  due  to  the 
accumulation  at  intervals  of 
lymph  or  periaxial  cement- 
substance  in  the  lymph-space 
between  the  cylinder-axis  and 
the  medullary  sheath  (Fig.  45). 
The  nerve-fibre  finally  loses 

its  medullary  sheath.  From  this  point  it  passes 
through  the  tissue  with  a  simple  covering  of  neuri- 
lemma and  occasional  nerve-corpuscles.  From  time 


NERVE- FUNICULUS  OF  THE 
TAIL  OF  A  MOUSE,  AFTER  IM- 
PREGNATION WITH  NITRATE  OF 
SILVER. — Large  flat  endothe- 
lial cells  are  seen  covering  its 
surface.  For  explanation  of 
the  small  crosses  see  preced- 
ing figure.  (Kanvier.) 


EXPLANATION  OF  PLATE  IX. 


Fig.  1.  Transverse  section  of  a  small  branch  of  a  cerebro- 

spinal  nerve.     Medium  enlargement. 

a,  Common  sheath  ;  b,  lymph-space  within  it ;  c,  perineu- 
rium carrying  bloodvessels,  v,  and  lymph-vessels ;  d,  axis 
cylinders  of  medullated  nerve  fibres.  These  fibres  are  col- 
lected together  into  bundles,  inclosed  within  a  sheath,  which 
consists  of  a  condensation  of  the  connective-tissue  of  the 
perineurium.  The  individual  nerve  fibres  constituting  such 
a  bundle  are  separated  from  each  other  by  a  delicate  tissue 
known  as  the  endoneurium. 

Fig.  2.  Minute  subdivisions  of  the  nerves  in  the  superficial 
layer  of  the  cornea,  termed  the  subepithelial  plexus,  as 
seen  in  the  cornea  of  a  Rabbit  after  treatment  with 
chloride  of  gold.  High  power. 


Fig.  3.  Connective-tissue  elements  of  the  perineurium  of  a 
cerebro-spinal  nerve.     Very  high  power.     (After  Kan- 
vier.) 
/,  Connective-tissue  bundles  ;  c,  fiat  connective-tissue  or 

endothelial -cells. 

Fig.  4.  A  minute  bundle  of  medullated  nerve-fibres  in  the 
tongue  of  a  Cat,  showing  axis-cylinders,  c,  and  nuclei 
of  the  neurilemma,  n.  High  power. 

Fig.  5.  Vertical  section  of  anterior  epithelium,  a,  b,  and 
superficial  layers,  e,  c,  of  the  fibrous  tissue  of  a  cornea 
stained  with  gold,  showing  the  penetration  of  the  nerve- 
filaments  between  the  corneal  epithelium,  and  the  forma- 
tion there  of  an  inter-epithelial  network  of  minute  nerve- 
fibres.  (After  Cohnheim.) 


PLATE     IX 


.4. 


Fif  S. 


NERVOUS    TISSUE. 


79 


to  time  the  axis-cylinder  splits  up  into  branches, 
which,  by  further  division,  become  so  small  as  to  be 
composed  of  an  extremely  small  number  of  fibrils 
loosely  bunched  together.  In  these  minute  divisions 
of  the  axis-cylinder  the  neurilemrna  ultimately  dis- 
appears, and  the  only  remains  of  the  original  en- 
velopes of  the  medullary  nerve-fibre  are  a  few  flattened 
connective-tissue  cells  which  at  scattered  points  wrap 
more  or  less  completely  around  the  small  bundles  of 
nerve-fibrils.  By  this  time  the  nerve  fibrils  have 
become  beaded  (fig.  2,  Plate  IX.).  After  the  axis- 
cylinder  has  lost  its  medullary  sheath  and  has 
branched  in  the  manner  above  indicated,  the  nerve- 
fibrils  are  frequently  collected  again  into  delicate 
fibrillar  bundles  to  form  networks.  Notwithstand- 
ing these  numerous  ramifications  and  anastomoses  of 
collections  of  minute  nerve-fibrils,  it  is  believed  that 
an  individual  fibril  itself  never  divides. 

Fibres  of  Remak.  —  Attention  has  thus  far  been 
called  to  three  different  forms  of  nerve-fibre.  It  is 
now  proposed  to  consider  a 
fourth  variety  —  the  gray  or 
gelatinous  fibre  or  the  fibre  of 
Remak.  This  does  not  sensibly 
differ  from  a  variety  of  medul- 
lary fibre  already  described, 
namely,  the  one  which  has 
lost  its  medullary  sheath,  and 
is  composed  simply  of  neuri- 
lemma,  nerve-corpuscle,  and 
axis-cylinder. 

In  the  cerebro-spiual  nerves 
the  medullated  fibres  greatly 
preponderate  over  the  non- 
medullated  or  gelatinoid 
fibres.  In  the  sympathetic 

J       f 


Fig.  48. 


NERVE-BRA*™ 


a 

A    SMALL 
"OM  THE  s™p*™  ™  * 

MAMMAL.  —  d.  Two   dark-bor- 

this     Order    is     Usually,       dere<l     nerve-tubes     among    a 
i.i  i  i  i         number  of   Remak's    fibres,  b. 

although  not  always,  reversed,     (Frey.) 
and  the  medullated  nerves  are 

frequently  finer  than  in  the  cerebro-spinal  nerves. 
In  nerves  of  a  mixed  character  the  sympathetic  fibres 
may  run  in  a  bundle  by  themselves  or  they  may  be 
indiscriminately  mixed  with  the  other  fibres.  Of  the 
medullated  nerves,  the  sensory  fibres,  as  a  rule,  retain 
their  medullated  sheath  longer  than  do  the  motor 
fibres. 


PERIPHERAL  TERMINATIONS  OF  NERVES. 

This  subject  may  be  considered  under  two  general 
heads  :  a,  the  peripheral  termination  of  sensory 
nerves  ;  and,  I,  those  of  motor  nerves. 


a.  Peripheral  terminations  of  sensory  nerves. — As 
has  been  already  indicated,  the  smallest  microscopic 
medullated  nerve  consists  of  a  perineurium  sur- 
rounding a  bundle  of  nerve-fibres.  Some  fibres  lose 
the  medullated  sheath  earlier  than  others.  When 
the  nerve  is  very  near  its  termination,  usually  the 
medullary  cylinder  and  the  neurilemma  disappear 
from  all  the  fibres  within  the  investing  perineurium. 
The  fibrils  of  the  different  axis-cylinders,  being  now 
more  free  than  before,  interlace  in  such  a  manner 
that  the  nerve-bundle  appears  much  like  a  longitudi- 
nal network  of  fibrils  collected  into  a  cord.  In  the 
skin  and  mucous  membranes,  near  the  surface,  and 
in  many  other  locations,  these  non-rnedullated 
branches  ramify  and  unite  into  a  plexus;  each  limb 
of  the  plexus,  even  when  it  comprises  not  more  than 
two  nerve-fibrils,  is  still  invested  by  a  delicate  mem- 
brane which  is  the  representative  of  the  perineurium. 
Along  the  course  of  these  ramifications,  and  especially 
at  the  nodal  points  of  the  plexus,  are  a  few  nuclei. 

Subepithelial  plexuses  and  networks. — In  the  skin 
and  mucous  membranes  a  plexus  exists  beneath  the 
epithelial  covering.  Hence  it  has  been  called  the 
subepithelial  plexus  or  ground  -  plexus.  From  this 
subepithelial  plexus,  single,  fine,  beaded  fibrils,  or 
small  collections  of  such  fibrils,  come  off  and  unite 
with  each  other  into  a  network  of  meshes  of  various 
sizes  and  outlines.  This  network  of  nerve-fibrils  is 
located  immediately  beneath  the  epithelium,  and  has 
consequently  been  called  the  subepithelial  nettvork 
(fig.  2,  Plate  IX.). 

Intercellular  networks. — Some  of  the  branches  of 
the  subepithelial  network  enter  the  layer  of  epithe- 
lium, passing  in  the  intercellular  cement  between  the 
epithelial  cells.  These  branches  ramify  among  the 
epithelia  to  form  an  intercellular  network  of  single- 
beaded  fibrils  (fig.  5,  Plate  IX.).  In  some  locations 
the  subepithelial  networks  are  peculiarly  arranged 
with  respect  to  the  direction  of  the  fibrils  and  the  con- 
sequent outline  of  the  meshes.  Beneath  the  epithe- 
lium of  the  cornea,  for  example,  the  branches  which 
come  from  the  ground-plexus  give  origin  to  ramifica- 
tions, which  with  the  stem  whence  they  arise  present 
an  appearance  that  has  been  compared  to  the  cat-o- 
nine-tails  (fig.  2,  Plate  IX.). 

There  is  a  great  diversity  of  opinion  as  to  whether 
the  nerve-fibrils  from  the  subepithelial  plexus  simply 
end  in  the  cement-substance,  between  the  epithelial 
cells,  in  a  network  such  as  above  indicated,  or  whether 
they  terminate  by  free  extremities,  some  of  which 
communicating  with  the  stellate  cells  among  the  epi- 
thelium, others  extending  to  the  surface. 


HISTOLOGY. 


It  seems  to  be  certain  that  some  of  the  nerves  of 
special  sense  terminate  among  epithelial  cells.  In 
the  Schneiderian  membrane  the 
olfactory  nerves  form  a  subepithe- 
lial  plexus,  fibres  from  which  ter- 
minate in  certain  rod-shaped  ele- 
ments (b,  Fig.  49),  the  superficial 
ends  of  which  reach  the  surface 
between  the  columnar  epithelial 
cells  of  that  membrane.  The  ter- 
minations of  the  optic  nerve  are 
conical  and  rod-like  organs,  which 
are  imbedded  between  epithelial 
cells.  The  auditory  nerves  prob- 
ably have  an  analogous  ending. 
The  gustatory  nerve  has  a  peculiar 
terminal  organ  (the  taste-bulb)  im- 
planted among  the  lingual  epithe- 
lium (Fig.  50). 

In  some  kinds  of  connective- 
tissue,  also,  sensory  nerves  seem 
to  end  in  complicated  nervous 
networks.  In  the  cornea,  for  ex- 
ample, besides  a  superficial  subepithelial  nerve-plexus, 
above  mentioned,  there  is  also  a  deep  plexus  which 
supplies  the  posterior  lamellas.  Fig.  1,  Plate  X.,  ac- 
curately represents  (according  to  Klein)  the  manner 
of  distribution  of  the  minute  beaded  fibrillse  to  a  deep 
stratum  of  the  cornea  of  a  rabbit,  a.  Is  a  part  of  the 
ground-plexus  (or  nerve  of  the  first  order) — a  bundle 
of  interlacing,  free  nerve-fibrillae,  inclosed  by  an  ex- 
tremely delicate  sheath,  representing  the  perineurium. 


CELLS  OF  THE  OLFAC- 
TORY Mucous  MEMBRANE. 
— a,  b,  c.  After  Schnl  tze. 
d,  e,f.  After  Lockhart 
Clarke. 


b.  Are  branches  from  the  ground-plexus  (or  nerves 
of  the  second  order)  still  possessing  an  investing 
sheath,  but  comprising  only  a  small  number  of  fibrils 
—  they  also  anastomose  to  form  a  network,  c.  Are 


FiK.  50. 


GUSTATORY  BULBS  FKOM  THE  LATERAL  GUSTATORY  OKOAN  OF  THE  RABBIT. — 
High  power.     (Strieker.) 

single,  minute,  beaded  fibrils  (nerves  of  the  third 
order),  which  arise  from  the  network  formed  by  b,  and 
pursue  a  rectilinear  course  among  the  fibrous  bundles 
of  the  connective-tissue — they  unite  with  fibres  of  a 
similar  appearance  to  form  a  network  of  rectangular 
meshes,  d.  Are  nerves  of  the  fourth  order,  still  finer 
beaded  isolated  fibrils,  which  arise  from  the  nerves 
of  the  third  order,  and  form  a  network  with  very 
small,  irregular  meshes.  The  fibrils  of  this  last 
minute  network  frequently  appear  to  be  in  contact 
with  some  part  of  the  surface  of  the  corneal  corpus- 
cles, the  analogues  of  connective- tissue  corpuscles. 
Opinion  is  evenly  divided  as  to  whether  this  last 
network  is  to  be  regarded  as  the  peripheral  termina- 
tion of  these  nerve-fibrils,  or  whether  still  more 


EXPLANATION  OF  PLATE  X. 


Fig.  1.  Represents  the  distribution  of  the  nerves  in  the  depth 

of  the  cornea.  Very  high  power.  (After  Klein.) 
a,  Nerve  of  the  first  order  ;  b,  nerve  of  the  second  order  ; 
c,  beaded  nerve  of  the  third  order,  forming  a  rectangular 
network  ;  d,  beaded  nerve  of  the  fourth  order,  which  forms 
a  network,  perhaps  upon  the  surface  of  the  branched  corneal 
corpuscles,  which  latter,  with  their  branches  (e)  and  their 
nuclei,  are  represented  in  the  figure. 

Fig.  2.  End  bulb,  b,  and  medullary  nerve,  c,  d,  of  the  con- 
junctiva of  a  Calf;  a,  axis-cylinder  termination  of  the 
nerve  within  the  bulb.  High  power.  (After  Krause.) 

Fig.  3.  Pacinian  corpuscle.     High  power. 

n,  Axis-cylinder  of  medullary  nerve-fibre  ;  e,  termination 


of  the  sheath  of  Schwann  in  the  fibrous  lamellae,  rf,  of  the 
Pacinian  body  ;  a,  c,  the  axis-cylinder ;  b,  its  division  and 
termination  near  the  end  opposite  the  entrance  of  the  nerve- 
fibre. 

Fig.  4.  Distribution  of  nerves  in  the  wall  of  a  small  arte- 

riole.     High  power.     (Arnold.) 

a,  Larger  nerve-twigs  which  branch  into  minute  subdivi- 
sions, some  of  which,  according  to  Arnold,  terminate  in  the 
nucleoli  or  within  the  nuclei,  c,  of  the  smooth  muscle-fibres 
of  the  tunica  media. 


Fig.  5. 


Shows  the  relations  of  the  minute  nerves  to  the  walls 
of  a  capillary  bloodvessel.    High  power.    (After  Klein.) 


PLATE     X 


Fig.  2 


Fig.  4. 


it.c. 


NERVOUS   TISSUE. 


81 


minute  fibrils  come  off  from  it,  and  enter  the  sub- 
stance of  the  corneal  corpuscles  to  terminate  therein. 

Besides  the  foregoing  modes  of  peripheral  distribu- 
tion of  sensory  nerves,  there  are  yet  to  be  men- 
tioned certain  special  structures  in  which  nerves  of 
this  character  frequently  end.  The  most  important  of 
these  are  the  Pacinian  corpuscles,  tactile  corpuscles, 
and  the  end-bulbs  of  Krause. 

End-bulbs  of  Krause. — These  organs  are  met  with 
in  small  numbers  at  the  peripheral  ends  of  some  of 
the  medullated  nerves  terminating  in  the  deeper 
layers  of  the  conjunctiva,  especially  near  the  cornea. 
They  appear  to  have  a  simple  plan  of  structure. 

b,  fig.  2,  Plate  X.,  represents,  under  a  low  power, 
the  simplest  form  of  such  an  end-bulb  from  the  con- 
junctiva of  the  calf.  In  this  case  its  outline  is  some- 
what cylindrical,  with  rounded  ends,  and  it  is  fixed 
upon  the  end  of  a  medullated  nerve-fibre,  c.  The 
nerve-fibre  is  seen  to  pass  nearly  straight  along  the 
axis  of  the  elongated  bulb,  and  to  terminate  in  a 
slightly  tapering  extremity,  near  the  end  opposite  the 
point  of  entrance.  In  man  the  end-bulbs  of  Krause 
are  often  more  or  less  spherical,  and  the  nerve-fibre, 
after  entering  the  organ,  instead  of  pursuing  a 
direct  course,  is  frequently  more  or  less  convoluted, 
and  even  sometimes  branched.  The  nerve-fibre  upon 
which  it  is  placed  possesses  a  distinct  perineurium, 
enveloping  a  neurilemma,  within  which  is  an  axis- 
cylinder  insulated  by  a  medullary  sheath  :  all  these 
parts  exhibit  their  usual  characteristics.  When  the 
nerve  reaches  the  end-bulb  the  perineurium  spreads 
out  and  envelops  it,  forming  in  some  instances  a 
slightly  laminated  sheath.  Ordinarily,  but  not  always, 
the  nerve-fibre  loses  its  medullary  sheath  upon  enter- 
ing the  bulb.  The  axis-cylinder  enters  the  body  of 
the  bulb  and  passes  to  the  opposite  end,  either  in 
a  straight  or  somewhat  wavy  course,  or  after  first 
forming  several  tortuous  curves  or  convolutions.  It 
in  ay  end  in  a  tapering  extremity,  extend  into  a  knot, 
or  divide  into  two  or  more  branches,  each  ending  in 
a  terminal  enlargement.  Among  the  convolutions 
nuclei  are  generally  found  in  some  numbers,  embedded 
in  a  slightly  granular  substance.  Occasionally  the 
medullated  sheath  continues  for  some  distance  along 
the  convolution. 

Bulbous  nerve-terminations  somewhat  similar  to 
those  above  described  are  found  in  considerable  num- 
bers upon  the  genital  organs. 

Tactile  corpuscles. — The  tactile  corpuscles  are  nerve- 
terminations  of  much  wider  distribution  than  the  end- 
bulbs  of  Krause,  and  are  somewhat  more  complex  in 
structure.     They  are  found  mainly  in  the  apex  of 
11 


papillae  of  the  skin,  and  because  of  their  location  in 
greatest  numbers  at  the  ends  of  the  fingers,  and  upon 
other  surfaces  endowed  with  the  most  delicate  sense 
of  touch,  they  have  been  called  tactile  bodies  or  cor- 
puscles. In  their  simplest  form  they  consist  of  an 
enlargement  shaped  somewhat  like  a  pine  cone  upon 
the  end  of  a  medullated  nerve-fibre.  (Fig.  51.)  The 

Fig.  51. 


TACTILE  CORPUSCLE. — A.  Side  view  of  a  papilla  of  the  hand.  a.  Cortical  layer. 
6.  Tactile  corpuscle,  with  transverse  nuclei,  c.  Small  nerve  of  papilla,  with 
neurilemma.  d.  Its  two  nervous  fibres  running  with  spiral  coils  around  the 
tactile  corpuscle,  e.  Apparent  termination  of  one  of  these  fibres.  B.  A  tactile 
papilla  seen  from  above,  so  as  to  show  its  transverse  section,  a.  Cortical 
layer.  6.  Nerve-fibres,  c.  Outer  layer  of  the  tactile  body,  with  nuclei,  d. 
Clear  Interior  substance.  From  the  Human  subject,  and  treated  with  acetic 
acid.  Highly  magnified.  (Gray.) 

perineural  sheath  of  the  fibre  thickens  and  spreads  out 
to  form  a  tolerably  thin  laminated  fibrous  covering 
or  capsule  for  the  touch-corpuscle.  The  main  con- 
tents of  this  capsule  are  large,  clear,  vesicular,  nucle- 
ated cells  frequently  flattened  from  above  downward, 
and  piled  one  upon  the  other  somewhat  like  the  disks 
of  a  Voltaic  pile.  The  medullated  nerve-fibre  pene- 
trates the  touch-corpuscle  at  its  deep  end,  sometimes 
losing  its  medullary  sheath,  sometimes  retaining  it 
for  some  distance  within  the  body  of  the  corpuscle. 
Upon  entering  the  body  of  the  tactile  corpuscle  the 
nerve-fibre  coils  around  the  surface  of  the  previously 
mentioned  cells  in  a  sort  of  ascending  spiral,  which, 
sinking  into  the  indentation  between  the  cells,  is 
ultimately  lost  to  view.  Fine  fibrils,  probably  con- 
tinuous with  the  axis-cylinder  of  the  coils  between 
the  cells,  wind  around  the  surface  between  the  coils, 
and  cause  an  appearance  of  fine  transverse  fibrillation. 
Exactly  how  the  nerve  fibrilloe  terminate  in  this  com- 
plex body  is  not  known. 

Pacinian  corpuscles. — The  Pacinian  corpuscles,  in 
which  some  medullated  sensory  fibres  end,  are  com- 
paratively large  ovoid  bodies,  which  in  favorable 
locations  are  distinctly  visible  to  the  naked  eye. 
They  are  most  frequently  found  in  the  subcutaneous 
and  submucous  loose  cellular  tissue,  and  in  the  loose 
connective-tissue  between  bundles  of  muscle-fibres. 


82 


HISTOLOGY. 


They  are  also  not  infrequently  present  in  serous  cov- 
erings. The  mesentery  of  the  cat  is  the  most  favorable 
position  in  which  to  study  them.  They  consist  of  a 
thick,  dense  capsule  formed  by  a  large  number  of  thin 
concentric  membranous  laminae  of  white  fibrous  tis- 
sue (Fig.  52,  and  fig.  3,  Plate  X.).  These  laminae  are 

Fig.  52. 


PACFMIAN  CORPUSCLE  with  its  system  of  capsules  and  central  cavity. — a.  Arte- 
rial twig,  ending  in  capillaries,  which  form  loops  in  some  of  the  intercapsular 
spaces  ;  one  penetrates  to  the  central  capsule,  b.  The  fibrous  tissue  of  the 
stalk  prolonged  from  the  nourilemma.  n.  Nerve-tube  advancing  to  the  central 
capsules,  there  losing  its  white  substance,  and  stretching  along  the  axis  to  the 
opposite  end,  where  it  is  attached  by  a  tubercular  enlargement.  (Gray.) 

slightly  separated  by  very  thin  strata  of  semifluid 
substance,  in  which  is  imbedded  an  extremely  thin — 
probably  elastic — film  consisting  of  a  single  layer  of 
flat  endothelial  cells.  In  sections  of  the  Pacinian  cor- 
puscle, such  as  the  figure  represents,  the  nuclei  of  these 
endothelial  cells  appear  as  rows  of  fusiform  bodies  be- 
tween the  concentric  lamella.  The  capsule  incloses  a 
narrow  axial  space  of  an  elongated,  somewhat  cylindri- 
cal-form, usually  having  a  slight  enlargement,  some- 
times even  a  bifurcation  of  the  upper  end.  This  capsule 
fits  over  the  extremity  of  the  nerve-fibre  in  the  follow- 
ing manner.  The  perineural  sheath  of  the  medullated 
nerve-fibre  thickens  and  becomes  continuous  with  the 
outer  lamellae  of  the  fibrous  capsule  of  the  corpuscle. 
The  sheath  of  Schwann  and  the  medullary  sheath 
are  generally  lost,  as  the  nerve-fibre  penetrates  the 
thickness  of  the  capsular  covering.  By  the  time 
that  the  axis-cylinder  has  reached  the  axial  space 
of  the  capsule  it  has  usually  lost  all  of  its  cover- 


ings. It  passes  up  the  central  portion  of  the  space 
until  the  enlargement  at  the  end  is  reached.  Here 
the  axis-cylinder  terminates  generally  in  a  single 
button-shaped  or  cauliflower  knob.  Sometimes  just 
before  reaching  this  point  the  axis-cylinder  bifurcates 
or  trifurcates,  each  division  ending  in  a  similar 
enlargement. 

Instead  of  the  axis-cylinder  pursuing  a  nearly 
rectilinear  course  in  the  axial  space  of  the  capsule 
it  may  be  more  or  less  convoluted.  Sometimes 
the  medullary  sheath  continues  into  the  lower  part 
of  the  axial  space.  This  central  space,  besides  con- 
taining the  terminal  ends  of  the  nerve-fibrils,  is  filled 
with  a  semifluid  albuminoid  substance.  Its  walls 
are  covered  with  a  layer  of  endothelial  plates.  It  is 
doubtful  whether  the  individual  fibrillae  of  the  axis- 
cylinder  terminate  in  the  upper  portion  of  the  axial 
space  by  free  extremities  with  a  minute  bulb,  or 
whether  they  end>  in  an  extremely  fine  terminal  net- 
work. 

Besides  a  nerve-fibre,  each  Pacinian  corpuscle  is 
supplied  with  a  minute  afferent  and  efferent  blood- 
vessel and  an  intermediato  capillary  plexus.  The 
bloodvessels  usually  enter  and  emerge  with  the  nerve- 
fibre,  but  sometimes  they  pass  into  the  capsule  at  the 
opposite  extremity.  The  capillaries  are  distributed 
between  the  lamellae  of  the  fibrous  capsule,  and  never 
reach  the  central  axial  space.  Occasionally,  instead 
of  one  Pacinian  body  being  connected  with  a  nerve- 
fibre,  as  is  usual,  the  fibre  may  divide  at  a  node  of 
Eanvier,  and  each  branch  end  in  a  Pacinian  corpuscle. 
The  group  of  corpuscles  is  then  often  connected  to- 
gether by  longer  or  shorter  bands  of  fibrous  tissue. 

Hair-bulls. — The  hair-bulbs  receive  the  termina- 
tions of  medullary  nerve-fibres,  and  are  sometimes 
exquisitely  sensitive. 

Nerve-endings  in  gland-cells.  —  Pfliiger,  among 
others,  has  carefully  studied  the  relations  of  nerves 
to  some  of  the  secreting  glands,  and  has  found  nerve- 
fibres  in  direct  connection  with  the  nuclei  of  cells  in 
the  acini,  and  even  in  the  ducts  of  glands.  Fig.  53 
shows  four  modes  of  direct  termination  of  nerve- 
fibres  in  gland-cells. 

b.  Termination  of  motor  nerves. — The  motor  nerves 
have  their  peripheral  endings  among  muscle-fibres. 

Nerve-endings  in  smooth  muscle. — In  smooth  muscles 
their  character,  distribution,  and  termination  are  not 
the  same  as  in  striped  muscle.  Non-medullated  nerve 
bundles  run  and  branch  in  the  loose  connective-tissue 
between  the  bundles  of  muscular  fibres.  They  are 
enveloped  in  a  cellular  sheath,  which  is  a  representa- 
tion of  the  perineurium,  and  they  are  composed  of 


NERVOUS   TISSUE. 


83 


interlacing  fibrils  which  have  no  medullary  sheath, 
or  sheath  of  Schwann,  but  are  covered  at  intervals 
by  flat  cells,  which  are  probably  the  remains  of  the 
nerve-corpuscles  belonging  to  the  medullary  sheath. 


MOPES  OF  TERMINATION  OF  THE  NERVES  IN  THE  SALIVARY  GLANDS. — 1  and  2. 
Brandling  of  the  nerves  between  the  salivary  cells.  3.  Termination  of  the 
nerve  in  the  nucleus.  4.  Union  of  a  ganglion-cell  with  a  salivary  cell.  5. 
Varicose  nerve-fibres  entering  the  cylindrical  cells  of  the  excretory  ducts. 
(PJHiger.) 

Such  branches  communicate  with  their  neighbors  to 
form  a  plexus — the  ground-plexus  of  Arnold.  From 
this  ground-plexus  come  oft'  smaller  branches  com- 
posed of  small  groups  of  individual  fibrils.  These 
smaller  branches  are  still  covered  by  a  cellular-sheath. 
They  also  unite  into  a  plexus,  which  envelops  the 
perimysium  of  primary  bundles  of  smooth  fibres — the 
intermediary  plexus  of  Arnold.  The  intermediary 
plexus  immediately  enveloping  the  muscular  bundles 
gives  off"  branches  composed  of  single  beaded  fibrils, 
which  enter  the  endomysiurn  and  unite  to  form  a  deli- 
cate network  surrounding  the  individual  muscle-fibres. 
Some  authors  claim  that  this  last  network  again  gives 


off  extremely  minute  fibrils,  which  penetrate  the 
muscle-cell  and  end  in  the  nucleus;  others  declare  the 
network  to  be  the  peripheral  termination  of  these 
nerve-fibres.  Occasionally  a  few  pear-shaped  enlarge- 
ments are  met  with  upon  the  fine  fibrils  of  this  last 
network. 

Fig.  4,  Plate  X.,  represents,  according  to  Arnold,  the 
nerve-supply  of  the  smooth  muscle-fibres  in  the  walls 
of  a  small  artery.  Non-medullated  bundles  of  fibrils, 
similar  to  those  of  the  ground-plexus  described  above 
for  smooth  muscles,  unite  to  form  a  ground-plexus 
in  the  tunica  adventitia.  (It  should  be  mentioned 
here,  in  passing,  that  in  the  nodes  of  these  ground- 
plexuses  of  nerves  in  smooth  muscle  there  are  often 
located  one  or  more  cells,  which  many  regard  as  gan- 
glion nerve-cells.)  This  ground  plexus  gives  origin 
to  minute  but  still  compound  branches,  which  them- 
selves again  unite  into  a  more  delicate  plexus — the 
intermediary  plexus.  This  last  plexus  gives  off' single 
fibrils  which  enter  the  tunica  media,  pass  between  the 
individual  rnuscle-cells,  and  unite  there  to  form  a  fine 
network.  The  same  difference  of  opinion  exists  as  in 
the  former  case  concerning  the  direct  connection  of 
the  nerve -fibrils  with  the  nuclei  of  the  muscle-cells. 
In  many  places  capillary  bloodvessels  are  surrounded 
by  networks  of  nerve-fibrils,  as  shown  in  fig.  5, 
Plate  X. 

Nerve-endings  in  striped  muscle. — The  termination 
of  motor  nerves  in  striped  muscle  is  peculiar.  The 
nerve-fibres  preserve  their  medullary  cylinder  and 
sheath  of  Schwann  until  they  enter  the  muscle- 
fibres.  According  to  the  investigations  of  the  most 
recent  authors,  each  individual  rnuscle-fibre  receives 
one  or  more  rnedullated  nerve-fibres.  The  nerve- 
fibre  passes  to  the  muscle-fibre  obliquely,  and  enters 
the  sarcolemma, — the  neurilemma,  or  sheath  of 


Fig.  54. 


a.  !>• 

MUSCULAR  FIBRES  OF  LACERTA,  WITH  THE  TERMINATIONS  OF  NERVES  IN  END-PLATES  OF  KBHSE.— a.  Seen  in  profile.  P.  The  nerve  end-plates.  s.  The  base  of 
the  plate,  consisting  of  a  protoplasmic  mass  with  nuclei,  b.  The  same  seen  in  face,  when  a  perfectly  fresh  fibre  is  examined,  the  nerve-ends  probably  being  still 
excitable,  c.  The  same  as  seen  two  hours  after  death  from  poisoning  by  curare.  Highly  magnified.  (Kuhne.) 


HISTOLOGY. 


Scliwann,  ending  in  and  being  continuous  with  the 
elastic  envelope  of  the  muscle-fibre  (Figs.  87  and 
54).  The  nerve-fibre,  composed  of  a  medullary  sheath 
and  axis-cylinder,  penetrates  the  sarcolemma  and 
passes  into  and  is  lost  in  a  large  flat  body,  located 
upon  the  substance  of  the  muscle-fibre,  called  the  end- 
plate  of  Kuhne.  Before  disappearing  in  the  substance 
of  this  end-plate  the  still  medullated  fibre  may  branch 
and  the  branches  ramify  upon  the  end-plate,  each  yet 
retaining  its  medullated  sheath.  Where  the  medul- 
lary sheath  ends,  the  axis-cylinder  spreads  out  into 
the  surface  of  the  end-plate,  and  is  soon  lost  to  view. 
The  end-plate  is  usually  more  or  less  granular,  and 
sometimes  contains  a  considerable  number  of  oval 
nuclei.  The  granular  appearance  is  generally  due  to 
the  presence  of  a  minute  reticulum,  which  may,  per- 
haps, be  continuous  with  the  fibrils  of  the  axis-cylin- 
der. The  nerve-fibrils  are  not  known  to  pass  into  j 
the  contractile  substance  of  the  muscle-fibre.  -Some  j 
authors  believe  they  have  seen  the  branches  of  the  j 
nerve-fibre  extend  upon  the  surface  of  the  sarcous 
substance  beyond  the  end-plate. 

Beale  denies  entirely  this  mode  of  ending  of  the 
nerves  in  striped  muscles,  and  substitutes  for  the  end 
plate  of  Krause  within  the  sarcolemma  a  simple  net- 
work of  medullated  nerve  fibres  with  a  number  of 
nuclei  in  the  meshes,  claiming  that  the  network  rests 
upon  the  outside  of  the  sarcolemma. 

NERVE-CENTRES. 

I 

The  nerve-centres  are  constituted  by  gray  or 
vesicular  nerve-substance,  and  white  fibrous  substance. 
The  latter  consists  of  nerve-fibres  in  most  respects 
similar  to  those  which  have  already  been  described 
when  considering  the  nerves,  but  they  have  no  defi- 
nite neurilemma.  The  nerve-fibres  will,  therefore, 
not  occupy  particular  attention  in  this  place. 

The  former,  the  gray  matter,  contains  special  cells 
of  peculiar  form  and  structure  which  have  been  called 
nerve-  or  ganglion -cells. 

Neuroglia.  — •  In  the  cerebro-spinal  nerve-centres 
both  nerve-fibres  and  nerve-cells  are  found  imbedded 
in  a  soft  finely-granular  variety  of  connective-tissue 
which  has  received  from  Virchow  the  special  name 
of  neuro'jlia.  In  the  gray  substance  of  the  cerebro- 
spinal  centres  it  is  possible,  as  we  shall  see  below, 
that  the  neuroglia  may  possess  peculiarities  of  func- 
tion which  are  probably  not  common  to  the  neuroglia 
of  the  white  substance.  The  neuroglia  of  the  latter 
consists  of  a  semifluid, -homogeneous  substance  con- 
taining a  network  of  extremely  minute  fibrils  which 


are  probably  of  an  elastic  nature.  At  occasional  in- 
tervals, among  this  minute  elastic  network,  are  to  be 
seen  branched  connective-tissue  corpuscles  whose  fine 
ramifications  are  in  communication  with  the  fine  net- 
work already  described.  These  branched  connective- 
tissue  corpuscles  are  known  as  neuroylia-cells.  Be- 
tween the  medullated  nerve-fibres  of  the  white  sub- 
stance the  minute  fibrils  of  the  neuroglia-network  have 
mainly  a  longitudinal  direction. 

In  the  gray  substance,  the  meshes  formed  by  the 
neuroglia-fibres  are  extremely  minute  and  are  quite 
irregular  and  sponge-like.  In  addition  to  the  neu- 
roglia-network above  mentioned,  there  is  superadded 
a  minute  network  of  fine  fibrils  which  are  derived 
from  the  branching  processes  of  the  ganglion  nerve- 
cells  present  in  large  numbers  in  the  gray  matter — a 
network  difficult,  if  not  impossible,  to  distinguish 
from  that  composed  of  simple  neuroglia-fibres.  This 
has  been  termed  the  nervous  reticulum  of  Gerlach. 
Some  investigators  add  to  the  neuroglia  of  the  gray 
substance  of  the  spinal  marrow  still  another  nervous 
reticulum,  w'hich  derives  its  minute  fibres  from  a  re- 
peated division,  in  the  posterior  portions  of  the 
cord,  of  nerve-fibres  from  the  sensory  roots.  In 
this  complex  neuroglia  of  the  gray  substance  the 
vessels,  the  ganglion-cells  with  their  branches,  and  a 
limited  number  of  medullated  fibres,  are  imbedded. 

Ganglion-cells. — The  ganglion-cell  is  contained  with- 
in a  small  lyrnph-space  in  the  neuroglia.  It  is  of  an 
irregular  outline  more  or  less  closely  corresponding 
to  the  shape  of  the  cell.  The  size  of  the  latter  is 
comparatively  large,  but  different  ganglion-cells  vary 
widely  in  their  dimensions.  Some  are  relatively  of 
enormous  volume.  The  largest  are  usually  found 
in  the  anterior  horns  of  the  spinal  cord,  and  in 
the  motor  centres  of  the  cerebrum.  They  also 

vary  greatly  in  form.     Some 
Fig.  55.  are   oval  without   processes 

(apolar)  ;  some  fusiform  with 
one  or  more  processes  at 
either  end  (bipolar);  but  the 
majority  of  them  have  many 
branches  which  may  come 
off  at  any  portion  of  their 
surface  (rmtltipolar).  The 
body  of  the  ganglion  -  cell 

STELLATE  NERVE-CELL,  from  the      contains      an      intra  -  cellular 
nucleus  cervicis  cornu  (posterior  . 

vesicular  column)  of  a  Foetus  of    network     of      fine     fibrils. 

six  months,  showing  the  minute  Nearly  all  the  prOGBSSBS  of 
reticulum  formed  by  the  dichoto-  in 

mons  branching  of  the  processes    these  cells  repeatedly  branch 

(nervous  retioulum  of  Gerlach).       dicllOtomOUslv         Until         the 
Miuniifled   420  diameters.     (Car- 
penter.) resulting        fibres       become 


NERVOUS   TISSUE. 


85 


extremely  fine,  when  they  form  a  minute  network 
in  the  neuroglia — the  nervous  network  of  Gerlach 
above  mentioned.  Each  one  of  these  branching  pro- 
cesses contains  a  continuation  of  the  intra-cellular 

Fig.  56. 


A  MEDIUM-SIZED  GANOLTON-CEM.,  from  the  anterior  horn  of  the  gray  matter  of 
tho  spinal  cord  of  a  Calf,  isolated  after  a  short  maceration  in  serum  containing  a 
little  iodine  in  solution.  Magnified  600  diameters.  Some  of  the  processes  (as 
at  b)  are  abruptly  broken  off;  a  is  tho  axis-cylinder  process  of  Deiters. 
(Strieker.) 

network,  the  meshes  of  which  are  narrow  and  greatly 
elongated  in  the  direction  of  the  length  of  the  process. 


The  fibres  of  the  reticula  of  the  processes  spread  out 
in  the  cell-body,  and  cause  the  latter  to  appear  to  be 
crossed  in  various  directions  throughout  its  substance 
by  fine  fibrillae  (Fig.  56,  and  refer  also  to  fig.  2,  Plate 
XL). 

In  the  motor  areas  of  the  cerebro-spinal  system 
are  found  large  multipolar  ganglion  nerve-cells,  of 
which  one  of  the  processes  differs  from  the  previously 
described  branching  processes  in  several  respects.  In 
the  first  place,  the  process  is  smaller  at  its  connection 
with  the  body  of  the  cell  than  are  the  others  (a,  Fig. 
56).  Secondly,  as  the  distance  from  the  cell  increases, 
so  also  the  process  enlarges,  until  finally  it  becomes 
surrounded  by  a  medullary  sheath  (a,  Fig.  43).  This 
process  has  been  called  the  axis-cylinder  process  of 
Deiters.  It  has  a  distinct  longitudinal  fibrillation. 
Those  branched  ganglion  nerve-corpuscles  which 
possess  an  axis-cylinder  process  of  Deiters  on  the 
one  hand  communicate  with  the  motor  nerve-fibres 
through  their  axis-cylinder  process,  whilst  on  the 
other  hand  they  are  united  intimately  with  the 
nervous  reticulum  of  Gerlach  by  means  of  their 
finely  branching  processes.  Each  ganglion-cell  con- 
tains near  its  central  portion  a  large  spherical  nucleus 
limited  by  a  double  -  contoured  membrane,  and 
inclosing  sometimes  one  or  more  distinct  brilliant 
nucleoli.  The  nucleus,  like  the  cell-body,  is  com- 
posed of  an  intra-nuclear  network  in  connection  with 
the  intercellular  reticulum.  In  the  meshes  of  these 
reticula  is  inclosed  a  soft  semifluid  substance  some- 
times holding  in  suspension  brownish-yellow  pig- 
ment-granules. As  has  been  already  indicated,  these 
ganglion-cells  are  suspended  in  lymph-spaces — the 
per'cellular  lymph- spaces  which  sometimes  even  in 
health  may  contain  a  small  number  of  lymph-cells. 
The  ganglion-cells  of  the  gray  matter  of  the  cerebro- 
spinal  centres  vary  greatly  in  size,  shape,  and  distri- 
bution. 

Gray  matter  of  the  spinal  cord. — In  the  spinal  cord 
they  are  smallest  in  the  posterior  portion  of  the  pos- 
terior gray  horns,  and  are  largest  in  the  lateral  portion 
of  the  anterior  horns.  Instead  of  being  scattered 
evenly  or  irregularly  throughout  the  gray  matter 
of  the  cord,  they  are  mostly  collected  into  certain 
well-known  groups  which  extend  up  and  down  the 
cord  and  form  columns  of  cells.  In  Fig.  57,  three 
such  groups  are  represented  in  the  anterior  horn — the 
so-called  internal,  anterior,  and  lateral  groups.  It  is 
thought  by  some  authorities  that  these  are  the  only 
ganglion-cells  of  the  spinal  cord  which  possess  axis- 
cylinder  processes,  and  a  direct  connection  with  medul- 
lated  nerve-fibres.  In  front  of  and  in  the  anterior 


\ 


86 


HISTOLOGY. 


portion  of  tbe  gelatinous  substance  in  the  posterior  horn 
is  another  column.  At  the  root  of  the  posterior  horns 
in  the  dorsal  region  there  is  still  another  column  of 
ganglion-cells  located  near  the  posterior  white  col- 
umns (Clarke's  column).  Around  the  central  canal  or 


its  remains  is  another  aggregation  of  ganglion-cells. 
The  finely-branched  ganglion  nerve-cells  of  the  poste- 
rior horns  possess  no  axis-cylinder  processes,  and 
are  iu  communication  with  the  nervous  network  of 
Gerlach  only  by  means  of  their  minute  branches. 


Fig.  87. 


TRAN3VE 


T.  •> 

jlttin 

:RSE  SECTION  OF  THE  GRAY  SUBSTANCE  op  THE  SPINAL  CORD  THROUOH  THE  MIDDLE  OF  THE  LUMBAR  ENLARGEMENT. — On  the  left  side  of  the  figure  groups  of 
large  cells  are  seen  ;  on  the  right  side,  the  course  of  the  fibres  is  shown  without  the  cells.     Magnified  13  diameters.     (After  J.  L.  Clarke.) 


In  the  cervical  region  of  the  cord  a  few  ganglion-cells 
are  found  in  the  white  columns  adjoining  the  lateral 
group  of  multipolar  cells  in  the  anterior  horns. 

Ependyma  of  the  cord. — Around  the  central  canal 
of  the  cord  the  neuroglia  of  the  gray  substance  be- 
comes a  little  more  dense  than  elsewhere,  and  the 
fibres  of  the  reticulum  have  an  arrangement  peculiar 
to  this  location.  They  follow  three  main  directions. 
Some  are  longitudinal,  parallel  with  the  axis  of  the 
canal;  others  are  concentric,  and  a  few  radiate  per- 
pendicular to  the  surface  of  the  canal.  The  radial 
fibres  are  continuous  with  fine  processes  of  ciliated 
columnar  epithelial  cells  which  line  the  surface  of 
the  central  canal  in  a  single  layer.  In  the  human 
adult  the  central  canal  is  rudimentary  below  the 
cervical  region  of  the  cord,  and  is  not  patulous. 
This  condensation  of  the  neuroglia  at  the  surface 
of  the  central  canal  constitutes  the  ependyma  of  the 
cord.  The  canals  and  various  ventricles  of  the  brain 
are  lined  by  a  similar  tissue  which  is  there  also 
known  as  the  ependyma,  and  is  invested  by  a  single 
layer  of  ciliated  columnar  cells  whose  deep  ends  di- 
vide into  processes  which  communicate  with  the  neu- 


roglia-fibres.  The  particular  arrangement  of  the 
nerve-fibres  and  the  nerve-cells  of  the  cord  will  be 
described  in  the  subsequent  chapters  of  this  work. 

Cortical  or  yray  matter  of  the  train. — In  the  cortex 
of  the  brain  the  gray  substance  presents  general 
microscopic  appearances  which  are  peculiar  to  it.  It 
seems  to  be  arranged  in  several  illy-defined  layers, 
one  passing  almost  insensibly,  and  by  small  grada- 
tions into  those  adjoining.  Fig.  3,  Plate  XI.,  very 
well  represents  a  view  of  the  cortex  of  the  human 
cerebrum  as  it  appears  when  ordinarily  prepared  for 
examination,  but  Fig.  58  gives  a  more  intelligible  dia- 
grammatic sketch  of  the  minute  anatomy  of  the  gray 
matter  covering  a  cerebral  convolution.  According 
to  Meynert,  "  speaking  generally,  the  cortex  presents 
five  Iamina3(see  Fig.  58).  The  first  orsuperficial  lamina 
(J)  is  principally  composed  of  an  evenly  punctated 
non-nervous  matrix,  with  a  few  small  stellate  cells, 
and  near  its  surface  numerous  fine  varicose  nerve-fibres 
decussating  in  all  directions.  The  second  (2)  is  a  layer 
of  close-set,  small  pyramidal  corpuscles.  The  third  (3) 
is  a  layer  of  large  pyramidal  corpuscles.  The  fourth 
(•i)  is  a  layer  of  small,  close-set,  irregular-shaped  cor- 


NERVOUS   TISSUE. 


87 


puscles;   and  the  fifth  (5)  is  a 
layer  of  fusiform  corpuscles. 

"  The  different  parts  of  the 
same  hemisphere  are  connected, 
first,  by  the  numerous  inter- 
communicating processes  of  the 
cells,  and  second,  by  a  system 
of  arcuate-fibres  (in,  Fig.  58)  of 
different  lengths  lying  imme- 
diately inside  the  cortex." 

Lockhart  Clarke  differs  some- 
what from  Meynert  in  his  de- 
scription of  the  general  cortex 
of  the  cerebrum.  He  recognizes 
seven  layers,  and  describes  them 
as  follows: — - 

"  Most  of  the  convolutions, 
when  properly  examined,  may 
be  seen  to  consist  of  at  least 
seven  distinct  and  concentric 
layers  of  nervous  substance, 
which  are  alternately  paler  and 
darker  from  the  circumference 
to  the  centre.  The  laminated 
structure  is  most  strongly 
marked  at  the  extremity  of  the 
posterior  lobe.  In  this  situa- 
tion all  the  nerve-cells  are  small, 
but  differ  considerably  in  shape, 
and  are  much  more  abundant  in 
some  layers  thau  in  others.  In 
the  superficial  layer,  which  is 
pale,  they  are  round,  oval,  fusiform,  and  angular, 
but  not  numerous.  The  second  and  darker  layer 
is  densely  crowded  with  cells  of  a  similar  kind,  in 
company  with  others  that  are  pyriform  and  pyra- 
midal, and  lie  with  their  tapering  ends  either  to- 
wards the  surface  or  parallel  with  it,  in  connection 
with  fibres  which  run  in  corresponding  directions. 
The  broader  ends  of  the  pyramidal  cells  give  off  two, 
three,  four,  or  more  processes,  which  run  partly 
through  the  white  axis  of  the  convolution,  and 
in  part  horizontally  along  the  plane  of  the  layer,  to 
be  continuous,  like  those  at  the  opposite  ends  of  the 
cells,  with  nerve-fibres  running  in  different  directions. 
The  third  layer  is  of  a  much  paler  color.  It  is  crossed, 
however,  at  right  angles  by  narrow  and  elongated 
groups  of  small  cells  and  nuclei  of  the  same  general 
appearance  as  those  of  the  preceding  layer.  These 
groups  are  separated  from  each  other  by  bundles  of 
fibres,  radiating  towards  the  surface  from  the  central 
white  axis  of  the  convolution,  and  together  with  thorn 


TRANSPARENT  SECTION  op  A 

FCRROW  OP  THE  THIRD  CEN- 
TRAL CONVOLUTION  op  MAX. 
Moderately  magnified.  1.  Lay- 
er of  scattered  small  cortical 
corpuscles.  2.  Layer  of  close- 
set,  small,  pyramidal,  cortical 
corpuscles.  3.  Layer  of  largo 
pyramidal  corpuscles.  4. 
Layer  of  small,  close-set, 
irregularly  shaped,  cortical 
corpuscles  (granule-like  for- 
mations). 5.  Layer  of  fusiform 
cortical  corpuscles,  m.  Me- 
dullary layer.  (Meynert.) 


form  a  beautiful  fanlike  structure.  The  fourth  layer 
also  contains  elongated  groups  of  small  cells  and 
nuclei,  radiating  at  right  angles  to  its  plane ;  but  the 
groups  are  broader,  more  regular,  and,  together  with 
the  bundles  of  fibres  between  them,  present  a  more 
distinctly  fanlike  structure.  The  fifth  layer  is  again 
paler  and  somewhat  white.  It  contains,  however, 
cells  and  nuclei  which  have  a  general  resemblance  to 
those  of  the  preceding  layers,  but  they  exhibit  only 
a  faintly  radiating  arrangement.  The  sixth  and  most 
internal  layer  is  reddish  gray.  It  not  only  abounds 
in  cells  like  those  already  described,  but  contains 
others  that  are  rather  larger.  It  is  only  here  and 
there  the  cells  are  collected  into  elongated  groups, 
which  give  the  appearance  of  radiations.  On  its 
under  side  it  gradually  blends  with  the  central  white 
axis  of  the  convolution,  into  which  its  cells  are  scat- 
tered for  some  distance. 

"The  seventh  layer  is  the  central  white  stem  or 
axis  of  the  convolution.  On  every  side  it  gives  off 
bundles  of  fibres,  which  diverge  in  all  directions,  and 
in  a  fanlike  manner  towards  the  surface,  through  the 
several  gray  layers.  As  they  pass  between  the  elon- 
gated and  radiating  groups  of  cells  in  the  inner 
gray  layers,  some  of  them  become  continuous  with 
the  processes  of  the  cells  in  the  same  section  or  plane, 
but  others  bend  round  and  run  horizontally,  both  in 
a  transverse  and  longitudinal  direction  (in  reference 
to  the  course  of  the  entire  convolution),  and  with 
various  degrees  of  obliquity.  While  the  bundles 
themselves  are  by  this  means  reduced  in  size,  their 
component  fibres  become  finer  in  proportion  as  they 
traverse  the  layers  towards  the  surface,  in  conse- 
quence, apparently,  of  branches  which  they  give  off 
to  be  connected  with  cells  in  their  course.  Those 
which  reach  the  outer  gray  layer  are  reduced  to  the 
finest  dimensions,  and  form  a  close  network  with 
which  the  nuclei  and  cells  are  in  connection. 

"  Besides  these  fibres  which  diverge  from  the 
central  white  axis  of  the  convolution,  another  set, 
springing  from  the  same  source,  converge  or  rather 
curve  inwards  from  opposite  sides,  to  form  arches 
along  some  of  the  gray  layers.  These  arciform  fibres 
run  in  different  planes — transversely,  obliquely,  and 
longitudinally — and  appear  to  be  partly  continuous 
with  those  of  the  diverging  set  which  bend  round,  as 
already  stated,  to  follow  a  similar  course.  All  these 
fibres  establish  an  infinite  number  of  communications 
in  every  direction,  between  different  parts  of  each 
convolution,  between  different  convolutions,  and  be- 
tween these  and  the  central  white  substance." 

The  cerebro-spinal  nerve-centres  are  enveloped  by 


88 


HISTOLOGY. 


membranous  structures,  which  will  be  especially  con- 
sidered hereafter.  They  carry  the  blood  and  lymph 
to  and  from  the  nervous  tissue.  In  the  white  and 
gray  substance  of  the  cerebro-spinal  centres,  the 
bloodvessels  of  all  sizes  run  in  lymph-channels.  The 
blood-capillaries  of  the  brain  are  some  of  the  smallest 
in  the  whole  organism.  The  capillary  vessels  are 
much  more  numerous  in  the  gray  than  in  the  white 
substance. 

SPINAL  NERVE-GANGLIA. 

As  is  well  known,  the  sensory  roots  of  the  spinal 
nerves  pass  through  a  collection  of  ganglion  nerve-cells 
before  uniting  with  the  anterior  roots  to  form  a  nerve 
of  double  function.  In  leaving  the  spinal  marrow, 
and  passing  out  of  the  spinal  canal,  the  nerves  per- 
forate the  frail  envelope  of  the  cord  without  receiving 
any  part  of  it  as  a  covering.  In  penetrating  the 
arachnoidal  and  the  dural  investment  of  the  cord, 
however,  the  roots  of  the  spinal  nerves  receive  fibres 
from  eacli  of  these  membranes,  and  are  consequently 
surrounded  by  an  inner  or  arachnoidal  and  an  outer 
or  dural  sheath,  which  form  respectively  a  subarach- 
noid  and  a  subdural  lymph-space  around  the  nerve- 
root,  each  entirely  separated  from  the  other ;  but 
communicating  freely  with  the  corresponding  space 
of  the  spinal  cord.  As  the  nerve-roots  pass  on  and 
unite  to  form  the  spinal  nerve,  the  dural  sheath  be- 


comes continuous  with,  and  is  represented  by,  the 
epineurium,  while  the  arachnoid  is  represented  by 
the  perineurium. 

The  spinal  ganglia  are  enveloped  in  fibrous  tissue 
arranged  in  a  manner  quite  analogous  to  that  of  the 
nerves.  Groups  of  ganglion-cells  are  surrounded  by 
a  laminated  connective-tissue  identical  in  structure 
and  continuous  with  the  perineurium  of  the  nerve- 
bundles.  The  ganglion  is  composed  of  a  larger  or 
smaller  number  of  such  groups  separated  and  held 
together  by  a  loose,  tough  connective-tissue  in  which 
small  arteries  and  veins  ramify.  This  represents  the 
epineurium  of  the  nerves,  and  is  continuous  with  it. 
The  ganglion-cells  constituting  a  group  are  separated 
from  each  other  by  a  variable  amount  of  delicate, 
loose  connective-tissue  very  similar  to  the  endoneu- 
rium  separating  the  individual  fibres  of  the  nerve- 
bundles  which  penetrate  between  the  ganglion-cells 
of  a  group.  In  this  endoneurium  capillary  blood- 
vessels course,  and  single  nerve-fibres  or  groups  of 
medullated  and  non-mcdullated  fibres  run  between 
the  ganglion-cells. 

Ganglion-cells. — The  yanylion  nerve-cells  are  com- 
paratively large,  and  of  divers  sizes  and  forms.  The 
prevalent  form  is  that  ef  an  oval  or  somewhat  pear- 
shaped  body,  with  one,  rarely  two  or  more  processes. 
This  large  nerve-cell  contains  one  large  spherical, 
generally  excentric,  nucleus,  containing  one  or  more 
refractile  nucleoli.  The  nucleus  is  enveloped  in  a 


EXPLANATION  OF  PLATE  XI. 


Fig.  1.  Represents  Iialf  of  a  transverse  section  of  the  spinal 
cord  of  Man  in  the  lumbar  region.  Very  slight  enlarge- 
ment. 

/,  The  anterior  median  fissure  ;  f,  the  posterior  median 
fissure  ;  d,  the  remains  of  the  central  canal  lined  with  colum- 
nar epithelium,  and  located  in  the  gray  commissure.  In 
front  of  the  latter  is  seen  the  decussation  of  the  white  fibres 
of  the  commissure  ;  c,  the  anterior  horn  of  the  gray  matter  ; 
a,  bands  of  nerve-fibres  issuing  from  the  anterior  horn  to 
form  the  anterior  root  of  a  spinal  nerve  ;  b,  posterior  root 
issuing  in  a  single  band  from  the  gray  matter  of  the  pos- 
terior horn  ;  m,  the  lateral  tract ;  t,  the  posterior  radical 
tract;  g,  the  column  of  Goll ;  the  fibres  of  the  two  latter 
together  form  the  posterior  column. 

Fig.  2.  Transverse  section  of  a  portion  of  the  external  an- 
terior border  of  the  gray  matter  of  an  anterior  horn  of 
the  spinal  cord  of  Man.      Highly  magnified. 
c,  Cross-sections  of  medullated  nerve-fibres  of  the  adjoin- 


ing white  substance  ;  a,  nuclei  of  the  neuroglia  of  the  gray 
matter;  n,  n,  nerve-fibres  running  in  the  gray  matter;  a 
multipolar  ganglion-cell,  finely  striated,  is  seen  imbedded  in 
the  gray  substance  ;  within  the  ganglion- cell  a  large  vesicular 
nucleus  containing  a  nucleolus  is  distinctly  visible. 

Fi<*.  3.  Vertical  section  of  the  cortex  of  a  cerebral  convolu- 

O 

tion  of  Man.     Medium  enlargement. 
a,  Cortical  layer  in  which  the  prevalent  direction  of  the 
connective-tissue  or  neuroglia-fibres  is  parallel  to  the  sur- 
face ;  b,  layer  of  small  club-shaped  nerve-cells ;  g,  layer  of 
larger  club-shaped  nerve-cells ;  c,  capillary  bloodvessels. 

Fi<r.  4.  A  surface  view  of  a  fibrous  lamella  of  the  cornea  after 

O 

treatment  with  silver  nitrate.     High  power. 
/,  s,  Lymph-spaces ;  n,  a  corneal  nerve-bundle  ensheathed 
in  a  covering  of  endothelial  cell-plates. 


PLATE     XI 


Fig.l. 


. 


n,' 


Fig  3 


Fig  4. 


^1* 


%' 

A  .  •    ' 

'  ... 

• 


.** 


T  Sintlair  kSon 


NERVOUS    TISSUE. 


89 


double-contoured  membrane,  and  contains  an  intra- 
nuclear network,  in  communication  with  an  intra-cel- 
lular  network  in  the  body  of  the  cell.  This  intra-cel- 
lular  network  continues  into  the  process.  The  latter 
may  be  regarded  as  an  axis-cylinder  process.  The 
ganglion-cell  is  enveloped  by  a  thin  homogeneous 
membrane  or  capsule,  which  is  continuous  with  the 
neurilemma  or  sheath  of  Schwann  of  the  nerve-fibre 
with  which  it  is  connected.  The  enveloping  mem- 
brane of  the  ganglion-cell  is  lined  by  granular,  flat- 
tened, somewhat  polyhedral  cells.  They  are  analo- 


NERVE-CEI.I.S  PROM  THE  GASSERIAX  GAXOLION  OF  THE  HUMAN  SFBJECT.— 
a.  A  globular  one  with  defined  border.  6.  Its  nucleus,  c.  Its  nucleolus.  d. 
('mutate  cell.  e.  Elongated  cell  with  two  groups  of  pigment-particles.  /. 
Cell  surrounded  by  its  sheath  or  capsule  of  nucleated  bodies,  g.  The  same, 
the  sheath  only  being  in  focus.  Magnified  300  diameters,  (dray.) 

gous  with  the  nerve-corpuscles  of  the  medullary 
sheath  of  a  nerve.  The  ganglion-cell  usually  fills  the 
space  formed  by  the  enveloping  membrane.  It  fre- 
quently contains  a  small  number  of  yellowish  or  dark- 
brown  pigment-granules  in  some  portions  of  the  cell- 
body.  Instead  of  the  ganglion-cell  being  unipolar, 
it  may  be  bipolar  or  even  multipolar. 

Fig.  60. 


STKi-nrriiE  OF  GANULIONIC  NERVE-CEIL. — A.   According  to  Dr.  Beale :    o, 
straight  process ;  c,  spinal  fibre.     B.  According  to  Arnold.     Highly  magnified. 

A,  Fig.  60,  represents,  according  to  Bcale,  a  pecu- 
liar form  of  bipolar  glanglion-cell  not  infrequently 
found  in  the  spinal  ganglia  of  frogs,  and  occasionally 
met  with  among  mammals.  It  differs  from  the  last- 
described  unipolar  cells  by  having,  in  addition  to  a 
12 


straight  axis-cylinder  process  similar  to  that  of  the 
common  unipolar  cell,  a  smaller  branch  which  winds 
more  or  less  spirally  around  the  larger  straight  pro- 
cess until  it  has  passed  a  little  distance  from  the  body 
of  the  cell,  when  it  leaves  the  straight  process  and 
turns  to  pursue  an  opposite  direction.  The  spiral 
turns  are  entirely  within  the  common  membranous 
envelope  of  the  cell.  The  straight  process  proceeds 
on  its  course  without  acquiring  a  medullary  sheath, 
while  the  spiral-fibre  soon  becomes  ensheathed  in  a 
medullary  cylinder.  Within  the  ganglia  the  nerve- 
fibres  arising  from  the  ganglion-cells  are  generally 
gray,  gelatinous  fibres  without  a  medullary  sheath ;  the 
latter,  nevertheless,  they  may  or  may  not  subsequently 
acquire.  The  bundles  of  nerve-fibres  which  pass  into 
a  group  of  ganglion-cells  spread  out  and  wind  around 
among  the  cells  to  emerge  again  after  losing  some 
fibres  and  gaining  others,  ultimately  to  end  in  their 
final  distributions. 


SYMPATHETIC  NERVE-GANGLIA. 

The  larger  ganglia  of  the  sympathetic  nervous 
system  do  not  essentially  differ  from  the  spinal  gan- 
glia, either  in  their  general  plan  of  construction  or  in 

Pig.  61. 


MICROSCOPIC  GANUI.ION  FROM  HEART  OF  THE  FROO.     (Strieker.) 

the  character  of  their  ganglion-cells.     They  need  not 
be  more  particularly  mentioned  here. 

Along  the  course  of  the  sympathetic  nerves  are 
found  single  ganglionic  cells  and  isolated  small  groups 
of  cells,  constituting  simple  microscopic  ganglia.  These 
microscopic  ganglia  and  isolated,  ganglion-cells  are  of 
quite  frequent  occurrence  in  the  nervous  plexuses 
supplying  involuntary  muscles,  as,  for  instance,  the 
unstriped  muscles  of  the  intestine,  the  walls  of  blood- 
vessels, and  the  heart.  The  ganglion-cells  are  usually 
located  at  or  near  the  nodal  points  of  the  nervous  net- 
work, the  larger  groups  being  found  in  the  ground- 
plexus,  or  compound  bundles  of  non-medullatcd  free 


90 


HISTOLOGY. 


axis-cylinders  contained  within  a  delicate  perineural 
sheath.  The  cells  are  within  the  perineurium  and 
among  the  nerve-fibrils  with  some  of  which  they  are 
continuous.  The  smallest  groups  and  isolated  cells 

Fig.  62. 


BIPOLAR  GANQLIONIC  CELLS  AND  NERVE-FIBRES  FROM  THE  GANOLION  OF 
FIFTH  PAIR  IN  THE  LAMPRET.    (Frey.) 

are  also  sometimes  situated  in  the  ground-plexus,  but 
they  are  frequently  located  at  the  nodal  points  of 
the  smaller  compound  bundles  of  free  axis-cylinders. 
These  ganglion-cells  are  found  to  present  the  same 
general  characters  as  those  of  the  large  sympathetic 
ganglia,  and  need  not  be  more  particularly  dwelt 
upon.  They  are  very  frequently  loaded  with  dark 
pigment-granules. 


THE  LYMPHATIC  SYSTEM. 

The  lymphatic  is  the  most  extensive  system  of  the 
organism,  and  one  of  the  most  important.  It  is 
mainly  by  the  way  of  the  lymph  that  the  nutritive 
supply  from  the  blood  ultimately  reaches  the  mor- 
phological elements  of  the  tissues,  for  only  a  very 
small  proportion  of  the  latter  are  brought  into  direct 
contact  with  the  blood-capillaries.  There  is  a  con- 
stant exudation  of  the  fluids  of  the  blood  through  the 
delicate  walls  of  its  vessels  into  the  neighboring 
lymph-spaces,  and  there  is  an  incessant  flow  from  the 
latter  towards  the  collecting  trunks  of  the  lymphatic 
system.  It  is  entirely  by  the  overflow  from  the 
blood  that  the  tissues  of  the  body  are  irrigated.  In 
comparison  to  the  velocity  of  the  blood,  the  lymph- 
current  is  extremely  sluggish.  It  is  impelled  princi- 
pally by  a  vis  d  tergo — the  slow  oozing  from  the  blood- 
vessels caused  by  the  centrifugal  pressure  upon  their 
walls  through  the  impetuous  rush  of  the  blood-tor- 
rent. It  is  aided  by  the  pressure  of  surrounding 
parts  in  movement,  and  to  some  extent  also  by  the 


action  of  muscle-fibres  which  sometimes  appertain  to 
the  lymphatic  system.  This  broad  though  sluggish 
stream  has  been  very  aptly  denominated  a  supplement 
of  the  blood-circulation. 

The  lymph  flows  in  channels  which  are  variously 
related  to  each  other,  and  to  the  different  components 
of  the  organism.  Their  structure  and  their  relations 
to  each  other  will  be  first  considered. 

The  lymph-passages  comprise  large  and  small 
trunks,  into  which  capillaries  empty,  and  which,  in 
their  turn,  receive  lymph  from  the  adjacent  inter- 
stices of  the  tissues,  the  latter  being  either  small 
lymph-spaces,  as  the  lymph  canalicular  system  of 
von  Recklinghausen,  or  large  lymph-cavities  like  the 
peritoneal,  the  pleural,  the  pericardial,  the  arachnoid, 
etc.  Along  the  course  of  the  lymph-current  are  in- 
terposed numerous  aggregations  of  a  peculiar  reticular 
tissue.  The  most  complex  arrangement  of  this  pecu- 
liar tissue  into  special  organs  is  found  in  the  so-called 
compound  lymphatic  glands,  such  as  those  of  the 
axilla,  the  groin,  the  mesentery. 

Large  lymph-vessels. — The  largest  lymphatic  trunks 
consist  of  a  wall  of  some  thickness  and  complexity  of 
structure.  This  wall  is  very  similar  to  that  of  veins. 
It  is  composed  of  three  coats — an  external,  middle, 
and  internal,  which  are  respectively  known  as  the 
tunica  adventitia,  the  tunica  media,  the  tunica  intirna. 
The  internal  coat  is  very  thin  and  delicate,  consisting 
of  an  inner  layer  of  endothelial  plates  similar  to  those 
of  veins;  of  an  external  layer  of  longitudinal  connec- 
tive fibres  and  a  few  elastic  fibres ;  and  of  a  middle 
layer  of  a  few  stellate,  flattened  corpuscles.  The 
tunica  media  contains  a  few  circular,  smooth  muscular 
fibres.  The  tunica  adventitia  is  composed  of  a  feeble 
network,  mainly  longitudinal,  of  fibrous  bundles  in- 
terspersed with  a  few  elastic  fibres,  also  united  into  a 
network.  Vasa  vasorum  and  nervse  vasorum  run 
in  the  tunica  adventitia,  and  ramify  in  the  tunica 
media. 

Small  lymph-vessels. — The  smaller  trunks  have  ex- 
tremely delicate  walls;  the  latter  are  reduced  to  a 
simple  endothelial  lining  of  the  lymph-channel.  By 
their  wall  simply  they  are  often  not  distinguishable 
from  the  lymph-capillaries.  When  empty,  in  conse- 
quence of  the  flabbiness  of  their  walls,  they  are  com- 
pletely collapsed,  and  their  cross-section  appears  as  a 
mere  slit  in  the  tissues.  When  distended,  these 
smaller  lymphatic  trunks  are  more  or  less  cylindrical 
in  form. 

Valves. — Lymphatic  trunks  are  distinguished  by 
the  presence  of  valves  at  frequent  intervals.  The 
valves  often  constitute  the  only  distinction  between 


THE   LYMPHATIC    SYSTEM. 


91 


small  trunks  and  capillaries.  They  consist  of  folds  of 
the  tunica  intima  projecting  into  the  lumen  of  the  ves- 
sel, usually  in  the  shape  of  two  hemispherical  sacs, 
which  rest  lightly  against  the  wall  of  the  vessel,  ex- 
cept when  the  lymph  attempts  to  flow  backwards. 
Then  they  project  into  the  lumen  until  the  opposite 
sacks  meet  and  form  a  kind  of  lymph-sac.  At  the 
location  of  these  valves  there  is  a  slight  bulging  out- 
ward of  the  lymphatic  walls.  Such  ampullar  en- 
largements along  the  lymphatic  trunks  are  very 
prominent  when  the  vessels  have  been  artificially  in- 
jected. In  the  small  lymph-trunks  the  lining  eudo- 
thelia  usually  have  somewhat  the  outline  of  a  long 
lozenge,  with  slightly  sinuous  edges.  The  smaller 
lymph-trunks  sometimes  anastomose  with  each  other, 
and  form  a  plexus. 

Lymph-capillaries. — The  small  lymphatic  trunks 
communicate  with  plexuses  of  lymph-capillaries. 
Lymph-capillaries  are  channels  through  the  tissues, 
with  walls  possessing  a  simple  endothelial  lining 
of  broad,  sinuous-edged  cells,  and  with  outlines  ex- 
Fig.  63. 


tremely  varied.  Their  lumen,  even  when  full,  may 
be  oval,  slit-like,  ampullar,  or  jagged.  Unlike  the 
capillary  bloodvessels,  which  they  enormously  exceed 
in  size  (fig.  3,  Plate  VII.),  they  are  frequently  larger 
than  the  trunks  into  which  they  empty.  Their  general 
direction  and  their  form  are  very  considerably  influ- 
enced by  the  arrangement  of  the  tissues  among  which 
they  lie. 

Until  the  investigations  of  von  Eecklinghausen, 
Klein,  Axel  Key,  Eetzius,  and  others,  in  recent  years 
threw  a  flood  of  light  upon  the  subject,  lymph-capil- 
laries were  considered  to  be  the  ultimate  ramifications 
of  the  lymphatic  system. 

Lyrnph-canalicular  system. — Von  Eecklinghausen 
demonstrated  a  connection  between  the  small  irregu- 
lar plasmatic  spaces,  existing  in  the  albuminoid,  semi- 
fluid cement,  in  which  the  connective-tissue  fibres  are 
imbedded,  and  the  lymphatic  capillaries.  These  ir- 
regular spaces,  with  their  canalicular  branches  and  the 
connective-tissue  cells  which  they  frequently  contain, 
von  Eecklinghausen  described  as  a  lymph- canalicular 


CORNEA  OF  THE  FROO  TREATED  WITH  LUNAR  CAUSTIC,  highly  magnified. — a.  Canalicular  systems.  la  one  place  a  branched  flattened  corneal  corpuscle  "with 
its  nucleus  is  seen ;  in  two  other  places  nuclei,  c,  of  corneal  corpuscles,  and,  d,  migrating  or  wandering  cells,  are  seen  in  the  lacunae  of  the  canalicular  system. 
b.  Branched  channels,  which  connect  the  lacuna:  of  the  canalicular  system.  (Carpenter.) 


system  (Fig.  63),  and  recognized  as  the  ultimate  radicles 
of  the  lymphatic  vessels.  By  their  branching  canali- 
culi  these  lymph-spaces  intercommunicate  with  one 
another,  and  those  nearest  the  lymph-capillary  open 
into  the  latter.  These  minute  lymph-spaces  among  the 
tissues  normally  may  contain,  as  we  have  already  seen, 
one  or  more  flattened  connective-tissue  corpuscles 
usually  applied  to  one  side  of  the  space.  They 
have  no  other  endothelial  lining.  In  those  spaces 
directly  communicating  with  a  lymph-capillary,  the 
connective-tissue  corpuscle,  by  one  of  its  processes,  is 


often  continuous  with  an  endothelial  plate  lining  the 
capillary.  The  point  of  communication  of  a  lymph- 
canaliculus  with  the  lumen  of  a  lymph-capillary  cor- 
responds to  an  opening  between  the  edges  of  the 
endothelium — a  stoma.  The  lymph-spaces  are  of 
extremely  variable  size  and  form.  Sometimes  stellate, 
sometimes  slit-shaped,  sometimes  more  or  less  cylin- 
drical, they  are  moulded  by  the  direction  of  the 
fibrous  bundles,  membranes,  or  other  tissues  in 
which  they  are  imbedded.  There  are  in  different 
portions  of  the  body  all  gradations  in  size  and  form 


HISTOLOGY. 


between,  minute,  more  or  less  stellate  lymph-spaces 
and  genuine  large  lymph-cavities,  whose  surfaces 
are  covered  with  a  complete  endothelial  lining.  Slit- 
like  spaces  are  frequently  found,  particularly  in 
laminated  fibrous  membranes,  lined  only  on  one  side 
with  a  complete  endothelial  layer. 

Relations  of  the  lymph-canalicular  system  with  lymph- 
capillaries  and  serous  cavities. — The  serous  cavities 
have  already  been  described.  They  are,  on  the  one 
hand,  in  communication  with  the  lymph-spaces  or 
lymph-canalicular  system  adjoining  them,  and,  on  the 
other  hand,  through  the  mediation  of  lymph-capilla- 
ries, are  directly  continuous  with  lymphatic  trunks. 
Von  Recklinghausen  first  demonstrated  the  commu- 
nication between  the  cavity  of  the  peritoneum  and 
lymphatic  trunks  of  the  diaphragm,  but  we  owe  our 
most  positive  knowledge  of  the  anatomy  of  the 
lymphatic  system  of  the  abdominal  and  thoracic  cavi- 
ties to  the  valuable  and  painstaking  labor  of  Klein. 

According  to  Klein,  the  peritoneal  surface  of  the 
centrum  tendineum  of  the  diaphragm  is  covered  by 
an  endothelial  lining,  whose  cells  have  not  all  the 
same  character  and  arrangement.  The  great  majority 
of  the  endothelia  are  ordinary,  thin,  elastic  cell- 
plates,  with  slightly  sinuous  outlines,  and  flat,  oval 
nuclei.  At  intervals  over  this  surface  are  clumps 
of  smaller,  polyhedral  granular  cells  (germinating 
endothelia),  with  sometimes  two  and  even  a  greater 
number  of  nuclei.  These  small  collections  of  germi- 
nating endothelia  surround  a  small  hole  in  the  serous 
surface.  The  holes  are  known  as  true  stomata,  in 
contradistinction  to  certain  small  groups  of  similar 
germinating  endotjielia  (pseudo-stomata)  in  which  no 
hole  is  apparent  (fig.  1,  Plate  I.).  The  centrum 
tendineum  consists  of  two  general  layers  of  fibrous 
bundles.  In  the  lower,  or  peritoneal  layer,  the 
bundles  have  a  direction  radiating  from  the  centre 
of  the  aponeurosis.  In  the  upper,  or  pleural  layer, 
the  fibrous  bundles  are  concentric.  Between  the 
fibrous  bundles  of  each  of  these  aponeurotic  layers 
is  a  system  of  lymph-capillaries.  Their  main  direc- 
tion is,  of  course,  the  same  as  that  of  the  fibrous 
bundles  between  which  they  run.  The  capillaries  of 
the  same  layer  occasionally  anastomose  with  their 
neighbors  by  lateral  branches,  and  the  two  systems 
also  intercommunicate  by  vertical  canals  running  from 
one  layer  to  the  other.  Now,  the  above-mentioned 
stomata  vera  are  located  upon  the  peritoneal  surface, 
over  the  spaces  between  the  radiating  fibrous  bundles 
of  the  lower  layer.  They  open  into  superficial,  small, 
vertical  canals,  which  lead  into  the  nearest  lymphatic 
capillaries.  Upon  the  pleural  surface  of  the  dia- 


phragm, over  the  interspaces  between  the  concentric 
fibrous  bundles  of  the  upper  aponeurotic  layer,  are 
also  numbers  of  stomata  vera.  These  latter  open 
by  short  vertical  lymph-channels  into  a  superficial 
plexus  of  lymphatic  trunks  between  the  basement- 
membrane  of  the  diaphragmatic  pleura  and  the  cen- 
trum tendineum.  This  superficial  plexus  of  lymph- 
atic trunks  is  provided  with  numerous  valves.  It  is  in 
communication  below  with  the  lymphatic  capillaries 
of  the  upper  layer  of  the  tendon  of  the  diaphragm, 
and,  as  a  consequence,  with  the  cavity  of  the  perito- 
neum. The  lymph  which  reaches  the  subpleural 
plexus  of  lymphatic  trunks  is  conducted  by  two  dif- 
ferent ways  into  the  general  circulation.  Over  the 
anterior  two-thirds  of  the  upper  surface -of  the  dia- 
phragm, the  lymph  is  drained  off  by  two  main  trunks, 
one  for  each  side,  which  pass  forward  to  the  anterior 
wall  of  the  chest,  and  ascend  behind  the  sternum  as 
far  as  the  manubriurn,  where  each  enters  a  lymphatic 
gland.  The  lymph  of  the  posterior  third  of  the  above 
plexus  is  conveyed  by  means  of  two  main  short 
trunks  directly  into  the  thoracic  duct.  The  move- 
ments of  respiration  cause  this  diaphragmatic  system 
of  lymphatics  to  act  somewhat  as  a  pump  in  draining 
the  peritoneal  cavity. 

Lymphatic  system  of  muscles. — In  the  aponeurotic 
sheath  of  muscles  it  has  been  found  that  the  inner 
and  outer  layers  each  possess  a  system  of  lymph- 
capillaries  which  bear  much  the  same  relation  to 
each  other  as  do  those  of  the  diaphragm.  The  outer 
plexus  of  lymphatic  capillaries  is  drained  by  lymph- 
trunks  with  numerous  valves.  The  lymph-capillaries 
and  lymph-spaces  of  the  endornysium  are  in  commu- 
nication, on  the  one  hand,  with  the  lymph-cylinders 
surrounding  the  ultimate  or  primary  muscle-fibre, 
and,  on  the  other  hand,  with  the  lymph-passages  of 
the  perimysium. 

Communications  of  the  cerelro-spinal  cavities. — The 
large  serous  cavities  of  the  cerebro-spinal  axis  have 
various  ramifications  and  connections.  The  space 
between  the  encephalon  and  the  inner  surface  of  the 
dura  mater  is  a  double  serous  cavity.  The  one  part 
of  this  cavity  is  separated  from  the  other  by  a  deli- 
cate partition — the  arachnoid.  The  space  between 
the  dura  mater  and  the  arachnoid  has  been  termed 
the  subdural  cavity;  while  that  between  the  arach- 
noid and  the  intima  pia  has  been  named  the  sub- 
arachnoid  cavity  of  the  cranium.  It  is  claimed  that 
the  one  has  no  communication  with  the  other.  Some 
authors  recognize  also  a  third  general  lymph-space 
existing  between  the  pia  mater  and  the  cerebral 
substance. 


THE    LYMPHATIC    SYSTEM. 


93 


Between  the  coverings  of  the  spinal  cord  there  are 
also  corresponding  lymph-cavities,  which  are  sepa- 
rated from  each  other  by  the  arachnoid,  namely,  the 
subdural  and  the  subarachnoid  cavities  of  the  cord. 
They  freely  communicate  with  the  corresponding 
cavities  of  the  brain.  The  external  surface  of  the 
dura  is  covered  with  endothelium,  as  are  also  the 
surfaces  of  the  large  lymph-spaces  of  the  cerebro- 
spinal  nervous  system. 

The  subarachnoid  cavity  of  the  brain  communi- 
cates with  the  ventricles  of  the  cerebrum.  The 
bloodvessels  from  the  arachnoid  pass  through  the 
pia  into  the  brain,  taking  a  lamina  of  the  arachnoid 
with  them  as  a  sheath  (the  perivascular  sheath),  the 
lymph -spaces  of  which  are  in  communication  with 
the  subarachnoid  space.  The  perivascular  sheath  of 
the  smallest  vessels  is  a  simple  layer  of  endothelium, 
partially  lining  a  perivascular  lymph-channel,  whose 
-wall  is  simply  the  surrounding  neuroglia.  The  lymph 
leaks  out  through  this  porous  wall  and  percolates 
among  the  minute  meshes  of  the  neuroglia-fibres  to 
reach  the  pericelhdar  lymph-spaces  surrounding  the 
ganglion-cells  of  the  gray  substance  and  the  peri- 
fibrillar  lymph-spaces  existing  between  the  neuroglia 
and  the  bare  medullated  nerve-fibres  of  the  white 
substance.  In  this  manner  the  ganglion-cells  and 
the  nerve-fibres  of  the  cerebrum  are  brought  into 
communication  with  the  subarachnoid  lymph-cavity 
of  the  cerebrum. 

An  essentially  similar  arrangement  of  the  lymph- 
circulation  exists  in  the  spinal  cord. 

Lymphatics  of  the  spinal  nerves. — While  considering 
the  minute  anatomy  of  the  spinal  ganglia,  occasion 
was  taken  to  refer  to  the  continuation  of  the  subdural 
and  subarachnoid  cavities  of  the  cord  into  the  spinal 
nerves :  the  subarachnoid  being  continuous  with  the 
perineural  lymph-space  of  the  nerve;  the  subdural 
communicating  with  the  epineiiral  lymph-spaces. 
The  endoneurium  between  the  individual  nerve-fibres 
contains  lymph  which  on  one  side  communicates  with 
spaces  around  the  nerve-fibres — on  the  other  with  the 
subperineural  space.  The  cranial  nerves  have  a 
lymph-circulation  similar  to  that  of  the  spinal  nerves. 
In  the  spinal  ganglia  the  epineural  and  the  perineural 
lymph-spaces  communicate  with  corresponding  spaces 
of  the  cord  and  of  the  nerve  to  which  they  are 
attached. 

Lymphatics  of  bloodvessels.  —  The  bloodvessels  of 
large  size  generally  possess  two  systems  of  lymphat- 
ics— one  for  the  tunica  intima  and  one  for  the  two 
outer  tunics.  Fig.  2,  Plate  XII.,  represents  the  lymph- 
canalicular  system  of  the  middle  or  connective-tissue 


layer  of  the  tunica  intima  of  a  large  arterial  trunk. 
The  tunica  adventitia  is  pre-eminently  a  trabeculated 
peri-vascular  lymph-space  which  is  in  free  commu- 
nication with  lymph-spaces  scattered  through  the 
tunica  media.  Besides  the  lymph-spaces  in  the  tunica 
adventitia,  the  vessel  may  be  partially  or  completely 
ensheathed  by  a  perivascular  lymph-space  (fig.  1, 
Plate  XII.),  or  be  surrounded  by  a  dense  plexus  of 
lymph-vessels. 

These  perivascular  lymphatics  frequently  commu- 
nicate with  the  lymph-canalicular  system  of  the  tissue 
through  which  they  pass.  Fig.  1,  Plate  XII.,  shows 
a  capillary  bloodvessel  having  such  a  relation  to  the 
lymph- spaces  of  the  surrounding  tissue.  A,  fig.  3, 
Plate  XII.,  is  a  faithful  reproduction  of  a  small  branch 
of  a  pulmonary  artery,  a,  and  an  accompanying 
lymphatic  capillary,  b,  which  communicates  with  the 
lymph-canalicular  spaces,  c,  in  the  inter-alveolar  septa. 
B,  same  figure,  gives  a  surface  view  of  the  inter- 
alveolar  lymph-spaces. 

Lymphatics  of  bones. — In  bones  the  lymph-canalic- 
ular system  is  represented  by  the  bone-corpuscles. 
By  their  canaliculi,  these  lymph-spaces  freely  open 
into  the  lymphatic  capillaries  of  the  Haversian  canals. 
The  Haversian  lymph-vessels  accompany  or  more  or 
less  completely  ensheathe,  as  perivascular  lymphatics, 
the  bloodvessels  of  these  canals,  and  in  their  turn 
communicate  with  the  lymph-vessels  of  the  peri- 
osteum. 

Lymphatics  of  cartilages. — Cartilage  also  possesses 
a  canalicular  lymphatic  system  which  directly  empties 
into  the  lymphatics  of  the  perichondrium.  The  ex- 
pansions of  the  lymph-canalicular  system  of  cartilage 
are  the  cartilage  capsules. 

Lymphatics  of  epithelial  structures. — Not  only  is  the 
lymph-canalicular  system  of  von  Eecklinghausen  in 
direct  open  communication  with  lymph-canals  and 
cavities  as  above  stated,  but,  according  to  Thoma, 
Arnold,  and  others,  the  intercellular  cement  between 
the  epithelia  of  the  skin,  mucous  membranes,  and 
glands,  and  between  the  endothelia  lining  the  lumen 
of  bloodvessels,  is  often  continuous  with  the  contents 
of  neighboring  lymph-spaces,  and  should  in  such  cases 
be  regarded  as  a  projection  of  the  lymph-canalicular 
system.  In  this  intercellular  cement,  circulation  is 
generally  very  slow,  but  nevertheless  quite  manifest. 
It  is  through  these  channels  that  minute  solid  par- 
ticles enter  the  subrnucous  lymphatics  of  the  air- 
passages  and  the  interalveolar  lymph-spaces  of  the 
air- vesicles  of  the  lungs.  The  probability  that  the 
minute  molecules  of  the  chyle  reach  the  capillary 
lacteals  of  the  villi  in  a  similar  manner,  and  that  for- 


94 


HISTOLOGY. 


eign  particles  injected  into  the  blood  pass  out  between 
the  cells  of  the  excreting  glands,  has  already  been 
alluded  to. 

LYMPHATIC  GLANDS. 

Lymph-glands  and  allied  reticular  or  lymphoid 
tissues,  important  parts  of  the  great  lymphatic 
system,  yet  remain  to  be  considered. 

Lymph- glands  are  more  or  less  complex  organs 
implanted  in  the  course  of  lymphatic  trunks,  and 
apparently  designed  for  the  elaboration  of  some  of 
the  colorless  elements  of  the  lymph.  They  may 
consist  of  simple  isolated  lymph-follicles,  or  of  an 
aggregation  of  them.  Since  a  large  lymph-gland  is 
practically  nothing  more  than  a  peculiarly-arranged 
aggregation  of  simple  lymph- follicles,  a  single  de- 
scription must  here  suffice. 

Lymph-glands,  such  as  those  of  the  axilla  or  mes- 
entery, are  more  or  less  ovoid  in  shape.  They  are 

Fig.  64. 


SECTION  OF  SMALL  LYMPHATIC  GLAND,  HALF  DIAQRAMMATICALI.Y  OIVEN,  WITH 
THE  CODR3E  OF  THE  LYMPH. — a.  The  envelope,  i.  Septa  between  the  follicles 
or  alveoli  of  the  cortical  part.  c.  System  of  septa  of  the  medullary  portion, 
down  to  the  hilus.  d.  The  follicles,  e.  Lymph-cords  of  the  medullary  mass. 
f.  Afferent  lymph-vessels,  the  different  lymphatic  streams  from  which  surround 
the  follicles,  and  flow  through  the  interstices  of  the  medullary  portion,  g.  Con- 
fluence of  these  to  pass  through  the  efferent  vessel  (h)  at  the  hilus.  (Frey.) 

enveloped  by  a  capsule  (Fig.  64),  which  generally 
consists  of  two  layers:  an  outer  layer  of  loose  con- 
nective-tissue, and  an  inner  lamellated  layer  of  dense 
fibrous  tissue.  Among  the  fibrous  bundles  of  these 
two  layers  are,  in  some  animals,  a  variable  number 
of  smooth  muscle-fibres.  Upon  one  side  of  the  gland 
two  or  more  large  lymphatic  trunks,  which  convey 
the  lymph  to  the  gland  (afferent  vessels'),  enter  the 
outer  layer  of  the  capsule  and  ramify  therein  to  form 
a  dense  plexus.  The  afferent  trunks  are  supplied 
with  circular  muscular  fibres  in  their  middle  tunic, 
and  with  numerous  valves.  At  the  opposite  side  or 
hilus  of  the  gland  a  number  of  small  vessels  unite  to 
form  a  large  trunk  which  receives  the  lymph  from 
the  gland  and  conveys  it  off  (the  efferent  vessel).  Upon 


examination  of  longitudinal  section  of  the  gland  made 
from  the  convex  surface  towards  the  hilus,  the  sec- 
tion appears  unevenly  colored  and  somewhat  mot- 
tled. The  central  third  is  of  a  deeper  red,  and  seems 
more  homogeneous,  while  the  outer  border  is  lighter 
colored  and  is  mottled.  The  inner  is  the  medullary, 
the  outer  is  the  cortical  portion  of  the  gland.  The 
minute  anatomy  of  the  organ  is  somewhat  different 
in  these  two  regions.  From  the  inner  surface  of  the 
dense  lamellated  inner  layer  of  the  capsule,  membra- 
nous partitions  or  septa  (I,  Fig.  64)  project  inwards  in 
such  a  manner  as  to  form  in  the  cortical  layer  a  series 
of  honeycomb-like  compartments,  which,  in  conse- 
quence of  the  fact  that  the  dividing  septa  converge 
towards  the  centre  of  the  gland,  are  more  or  less 
conical  with  the  bases  outward.  When  these  septa 
reach  the  medullary  area,  they  break  up  into  a  large 
number  of  thinner  or  thicker  bands  or  trabeculse, 
which  branch  and  anastomose  with  one  another  so 
as  to  form  a  loose,  sponge-like  network.  The  meshes 
of  this  medullary  inter-trabecular  network  communi- 
cate with  each  other  and  with  the  conical  compart- 
ment of  the  cortical  layer.  The  membranous  septa 
between  these  compartments  are  often  incomplete. 

The  conical  compartments  of  the  cortical,  or  fol- 
licular  layer,  as  it  has  been  called,  are  more  or  less 
completely  filled  by  a  pear-shaped  cellular  mass,  the 
so-called  follicle  (d,  Fig.  64).  At  the  border  of  the  me- 
dullary portion  of  the  gland  this  cellular  mass  tapers 
down  to  a  narrow  stem,  which  passes  into  the  inter- 
trabecular  spaces,  and  becomes  a  medullary  cylinder, 
or  cord  (e,  Fig.  64).  In  the  medullary  portion  of  the 
gland  the  medullary  cylinders  branch  and  anastomose 
in  a  complex  manner  to  form  an  irregular  network 
of  cellular  cylinders. 

The  cortical  follicles  and  the  medullary  cylinders 
consist  of  a  reticular  or  adenoid  tissue  permeated  by 
a  rich  network  of  blood-capillaries.  They  do  not 
entirely  fill  the  spaces  in  which  they  lie,  but  are 
separated  from  the  septa  of  the  cortex,  and  the  tra- 
beculse of  the  medullary  portion  by  a  lymph-sinus  of 
considerable  size.  The  lymph-sinuses  surrounding 
the  cortical  follicles  are  continuous  with  those  which 
surround  the  medullary  cylinders.  The  afferent 
lymph-vessels  ramifying  in  the  capsule,  as  above 
described,  penetrate  the  inner  laminated  layer  of  the 
capsule  and  open  freely  into  the  cortical  lymph- 
sinuses.  The  efferent  lymphatic  trunks  (g,  h,  Fig. 
64)  of  the  hilus  directly  communicate  with  the 
lymph-sinuses  enveloping  the  medullary  cylinders. 
The  free  course  of  the  lymph  is,  therefore,  from  the 
afferent  vessels  of  the  capsule  into  the  cortical  peri- 


THE    LYMPHATIC    SYSTEM. 


95 


follicular  sinuses,  thence  through  the  medullary 
sinuses  into  the  collecting  trunks  which  empty  into 
the  efferent  vessels  emerging  from  the  hilus. 

The  flow  of  the  lymph  through  these  sinuses  is 
greatly  impeded  by  innumerable  fine  fibres  united 
into  a  network  which  crosses  the  space  from  the 
follicles  to  the  septa  in  the  cortical  region,  and  from 
the  medullary  cylinders  to  the  trabeculae  in  the 
medullary  portion  (c,  Fig.  65).  The  fibres  of  this 

Fig.  65. 


IX 


PORTION  OF  THE  METHTT.ARY  STBSTANOE  OF  THE  MESENTERIC  GLAND  OF  AN 
Ox. — The  artery  injected  with  chromate  of  lead.  Highly  magnified,  a.  Medul- 
lary cylinder  with  capillary  network,  fine  reticulum  of  connective-tissue,  and 
a  few  lymph-corpuscles.  6,  6.  Superficial  lymph-path  or  medullary  sinus  tra- 
versed everywhere  by  a  reticulum  of  nucleated  cells.  This  reticulum  has  been 
represented  only  at  c,  with  numerous  anastomosing  prolongations.  The  lymph- 
corpuscles  have  for  the  most  part  been  removed  with  a  earners-hair  brush, 
rf,  d.  Trabeculfe,  composed  almost  exclusively  of  unstriped  muscular  tissue. 
A  small  medullary  cord  or  bridge,  containing  a  bloodvessel  and  numerous 
lymph-corpuscles,  is  shown  at  the  left  of  the  figure  as  springing  from  the  me- 
dullary cylinder.  (Strieker.) 

reticulum  are  hyaline,  and  present  every  variation  in 
shape  from  the  flattened  band  to  the  cylinder.  At 
their  nodal  points  they  slightly  enlarge,  and  very 
frequently  a  flattened  oval  nucleus  is  seen  at  these 
enlargements.  The  reticulum  consequently  appears 
to  be  formed  by  a  network  of  large  stellate  cells  re- 
sembling branched  connective-tissue  corpuscles.  But 
in  the  adult  tissue  this  is  an  illusion.  The  nuclei  be- 
long to  flat  endothelial  plates  which  closely  invest 
the  fibres  of  the  reticulum.  Every  part  of  the  surface 
of  the  lymph-sinuses  above  described  is  lined  with  a 
complete  layer  of  endothelial  plates.  They  cover  the 
reticular  partitions  as  well  as  the  septa  and  trabecula? 
on  the  one  side,  and  the  surface  of  the  follicles  and 
cylinders  on  the  other. 

Each  of  the  coarse  meshes  of  this  reticulum  in  the 


lymph-sinus  contains  two  or  more  lymph-corpuscles 
which  quite  fill  it. 

The  cortical  follicles  and  the  medullary  cylinders 
have  the  same  constitution.  They  consist  of  a 
reticulum  of  a  construction  very  similar  to  that  of 
the  lymph-sinuses.  But  the  fibres  which  form  it  are 
very  much  more  delicate,  and  the  meshes  are  much 
smaller.  At  some  of  the  nodal  points  of  this  reticulum 
a  flattened  ovoid  nucleus  may  be  seen.  As  in  the 
former  case,  these  flattened  nuclei  belong  to  endo- 
thelial plates  resting  upon  the  fibres.  In  the  follicles 
and  cylinders,  however,  the  surfaces  of  the  reticulum 
are  not  completely  covered  with  endothelial  cells. 
The  small  meshes  of  this  reticulum  are  closely  packed 
with  one,  two,  or  more  lymph-corpuscles  which  are 
usually  of  the  smallest  size,  consisting  of  a  large 
round  nucleus  surrounded  by  a  minimum  amount  of 
cell-protoplasm.  They  are  supposed .  to  be  young 
developing  lymph-cells. 

The  fine  reticulum  of  the  follicles  and  cylinders 
is  permeated  by  a  rich  network  of  capillary  blood- 
vessels (Fig.  65).  The  walls  of  these  capillaries  are 
enveloped  "by  and  connected  with  the  fibres  of  the 
reticulum  (fig.  6,  Plate  VI.). 

Besides  a  lymph-current  in  the  sinuses  from  the 
afferent  towards  the  efferent  vessels,  there  is  also  a 
current  in  the  follicles  and  cylinders  setting  outwards 
from  the  blood-capillaries  towards  the  surrounding 
perifollicular  and  pericylindrical  sinuses.  The  latter 
current,  aided  by  the  amoeboid  movements  of  the 
cells,  washes  the  lymph-corpuscles  from  the  follicles 

Fig.  66. 


1.  Rp.Tlcrji.AR  TISSUE,  from  a  lymphoid  follicle  of  the  vermiform  appendix 
of  the  rabbit,  with  the  system  of  meshes,  and  remains  of  the  lymph-cells  n. 
Most  of  the  latter  have  been  removed  artificially.  fi.  Lymph-vessel.  2. 
Longitudinal  section  of  a  Lieberkiihn's  gland,  showing  the  surrounding  retic- 
nlar  tissue.  In  the  meshes  of  this  are  seen  the  lymph-cells  a.  b.  Luinen  of 
a  vessel,  c.  Lumen  of  the  gland.  (Frey.) 

and  cylinders  out  into  the  surrounding  sinuses,  and 
the  current  in  the  latter  finally  carries  the  cells  into 


96 


HISTOLOGY. 


the  efferent  vessels.  The  meshes  of  the  reticulurn  of 
the  sinuses,  and  especially  those  of  the  follicles  and 
cylinders,  are  so  packed  with  lymph-corpuscles  that, 
in  sections  ordinarily  prepared,  nothing  can  be  seen 
but  the  crowd  of  cells.  In  order  that  the  reticula 
may  become  visible,  it  is  necessary  to  gently  pencil 
the  sections  with  a  camel's-hair  brush  or  to  persist- 
ently shake  them  in  a  fluid  medium.  When  this  pro- 
cedure is  successful,  a  thin  section  of  the  medullary 
portions  presents  a  picture  very  well  reproduced  in 
Fig.  66. 

The  arteriolcs  and  venules  which  communicate  with 


the  capillaries  of  this  tissue  run   in   the  septa  and 
trabeculas. 

Reticular  tissue  (adenoid  tissue  of  His)  is  a  lymphoid 
tissue  which  has  its  perfect  type  in  the  structure  of 
the  follicles  and  medullary  cylinders  of  lymph-glands. 
It  is,  therefore,  unnecessary  to  describe  it  more  par- 
ticularly in  this  place.  It  is  present  in  a  diffuse  form 
in  the  mucous  membrane  of  the  intestine  and  of  other 
localities.  It  is  met  with  in  serous  cavities  in  the 
form  of  patches  and  cords  of  variable  extent,  and  it 
is  found  in  numerous  other  localities. 


EXPLANATION  OF  PLATE  XII. 


Fig.  1.  A  silver  preparation  of  a  pencilled  omentum  of  a 
Rabbit,  showing  relations  of  blood-  and  lymph-vessels. 
High' power.  (After  Klein.) 

t>,  A  venule  filled  with  blood-corpuscles  ;  the  venule  givss 
off  capillary  branches  ;  I,  lymphatic  capillary,  .invaginating 
the  bloodvessels,  and  lined  with  endothelium,  the  outlines  of 
which  are  mapped  out  by  the  serrated  dark  lines  ;  s',  branches 
of  the  lymph-vessels  in  some  places  communicating  with  the 
neighboring  lymph-spaces. 

Fig.  2.  Internal  tunic  of  the  Human  aorta,  treated  with  sil- 
ver.    High  power.     (After  Langhans.) 
a,  Superficial  lymph-spaces  ;  b,  deeper  lymph-spaces  ;  both 


freely  intercommunicate,  and  are  separated  from  one  anollier 
by  the  ground-substance,  g. 

Fig.  3.  A.  From  a  section  of  a  Guinea-pig's  lung,  which  had 
been  injected  with  silver  nitrate,  showing  the  relations 
of  blood  and  lymph-vessels.     High  power, 
a,  Branch  of  pulmonary  artery  ;  I,  lymph-vessel  lined  with 
endothelial  plates,  and  in  connection  with  the  lymph-canali- 
cular  system  or  inter-alveolar  lymph-spaces,  c,  of  the  walls  of 
the  alveoli. 

B.  Same  lung,  showing  the  inter-alveolar  lymph-spaces, 
in  surface.     (After  Klein.) 


PLATE    XII 


.  2 


T.  S,nclMTlSOI-  lilh. 


PROSPECTUS 


A  SYSTEM  OF  HUMAN  ANATOMY, 


INCLUDING     ITS 


MEDICAL  AND  SURGICAL   RELATIONS. 


HARRISON    ALLEN,    M.  IX, 

PROFESSOR   OF   PHYSIOLOGY   IN   THE    UNIVERSITY   OF   PEXXSYI.YA.VIA,   ETC.,   ETC. 

WITH 

A    CHAPTER    ON    HISTOLOGY, 


E.    O.    SHAKESPEARE,    M.   D., 

OPHTHALMOLOGIST     TO     THE     PHILADELPHIA     HOSPITAL. 


To  be  completed  in  Six  Sections,  containing  about  jjo  pages  of  letter-press,  illustrated  with  jSo  figures  on  109  plates,  many  of  which  are 
beautifully  colored.      The  drawings  by  Hermann  Fabcr.  from  dissections  by  the  Author.     Also,  250  woodcuts  in  the  text. 


PRICE  PER  SECTION,  $3.50. 


Section       I.     HISTOLOGY.  Section  IV.     ARTERIES,  VEINS 'AND  LYMPHATICS. 

II.     BONES  AND  JOINTS.  V.     NERVOUS  SYSTEM. 

III.     MUSCLES  AND  FASCIAE.  "         VI.     ORGANS  OF  SENSE,  OF  DIGESTION  AND   GENITO-URINARY  ORGANS. 


The  plan  and  scope  of  the  work  may  be  gathered  from  the  following  brief  extract  from  the  introduction. 

"  It  is  the  design  of  this  book  to  present  the  facts  of  human  anatomy  in  the  manner  best  suited  to  the  requirements  of  the  student 
and  practitioner  of  medicine.  The  author  believes  that  such  a  book  is  needed,  inasmuch  as  no  treatise,  as  far  as  he  knows,  contains,  in 
addition  to  the  text  descriptive  of  the  subject,  a  systematic  presentation  of  such  anatomical  facts  as  can  be  applied  to  practice. 

A  book  which  will  be  at  once  accurate  in  statement  and  concise  in  terms;  which  will  be  an  acceptable  expression  of  the  present 
state  of  the  science  of  anatomy;  which  will  exclude  nothing  that  can  be  made  applicable  to  the  medical  art,  and  which  will  thus 
embrace  all  of  surgical  importance,  while  omitting  nothing  of  value  to  clinical  medicine, — would  appear  to  have  an  excuse  for  existence 
in  a  country  where  most  surgeons  are  general  practitioners,  and  where  there  are  few  general  practitioners  who  have  no  interest 
in  surgery." 

As  a  brief  introduction  to  the  essential  features  of  the  volume,  attention  is  invited  to  the  kinds  of  knowledge  of  the  human 
body  which  the  physician  demands. 

First.  An  exact  acquaintance  with  the  form  and  construction  of  the  organs  of  the  body.  But,  inasmuch  as  an  anatomical  fact  is 
of  little  use  unless  the  range  of  application  of  the  fact  is  known,  the  due  connection  between  the  normal  condition  of  the  organs  and  their 
variations  within  the  limits  of  health  will  receive  proper  attention,  accordingly  the  typical  description  of  each  organ  will  be  followed 
by  a  brief  statement  of  such  variations. 

Second.  The  physician  demands  a  knowledge  of  the  relations  of  the  parts.  This  information  it  is  necessary  to  possess  in 
performing  operations  and  in  explaining  signs  and  symptoms. 

Third.  The  physician  needs  some  account  of  the  uses  of  the  organs.  This  subject  overlaps  physiological  anatomy.  That  much 
only  will  be  succinctly  given  as  may  be  said  properly  to  illustrate  the  subject  from  an  anatomical  point  of  view,  and  at  the  same  time 
be  free  from  controversy. 

Fourth.  The  physician  must  have  a  true  conception  of  the  nature  and  general  behavior  of  morbid  processes,  and  of  the  manner 
in  which  such  processes  are  modified  by  locality.  His  comprehension  of  the  changes  due  to  diseased  action  in  a  given  place  must  be 
fairly  proportional  to  his  knowledge  of  the  normal  anatomy  of  that  place.  This  subject,  which  will  receive  the  name  of  localization  of 
diseased  action,  will  be  illustrated  for  the  most  part  by  concise  statements  of  recorded  cases,  in  which  the  essential  feature  of  each  case 
will  be  emphasized,  and  the  bearing  it  has  on  the  subject  treated  of  clearly  shown.  In  presenting  anatomical  features  in  explanation 
of  given  lesions,  or  of  signs  or  symptoms,  care  has  been  taken  to  give  the  sources  of  the  statements  made.  ' 

"Among  other  matters,  the  book  will  be  found  to  contain  an  elaborate  description  of  the  tissues;  an  account  of  the  normal 
development  of  the  body;  a  section  on  the  nature  and  varieties  of  monstrosities;  a  section  on  the  method  of  conducting  post-mortem 
examinations;  and  a  section  on  the  study  of  the  superficies  of  the  body  taken  as  a  guide  to  the  position  of  the  deeper  structures.  These 
will  appear  in  their  appropriate  places,  duly  subordinated  to  the  design  of  presenting  a  text  essentially  anatomical." 

In  the  preparation  of  this  elaborate  work  no  pains  have  been  spared.  The  illustrations  of  normal  anatomy,  with  a  few  exceptions, 
are  from  original  dissections,  engraved  on  the  stone,  with  the  name  of  every  part  clearly  drawn  upon  the  figure  after  the  manner  of 
"Holden"  and  "Gray,"  and  in  every  typographical  detail  it  has  been  the  effort  of  the  publishers  to  render  the  volume  worthy  of  the 
distinguished  position  anticipated  for  it. 

Each  section  will  be  enclosed  in  an  individual  portfolio,  thus  preserving  all  in  a  perfect  condition  in  case  it  is  subsequently 
desired  to  bind  them  as  a  volume. 


FOR   SALE    BY   SUBSCRIPTION    ONLY. 


REYNOLDS'    SYSTEM    OF    MEDICINE.      Revised  Edition.     Now  Ready. 

•V  SYSTEM  OF  MEDICINE.  Edited  by  J.  RUSSELL  REYNOLDS,  M.I).,  Professor  of  the  Principles  and  Practice  of  Medicine  in 
University  College,  London.  With  notes  and  additions  by  HENRY  HARTSHORNE,  M.  D.,  late  Professor  of  Hygiene  in  the 
University  of  Pennsylvania.  In  three  large  and  handsome  royal  octavo  volumes,  containing  3056  double-columned  pages,  with 
317  illustrations.  Per  volume,  cloth,  $5  ;  leather,  $6;  half  Russia,  §6.50.  Per  set,  cloth,  $15  ;  leather,  $18;  half  Russia,  $19.50. 

The  labors  of  the  American   editor,  Dr.   Hartsborne,  have  been  very  conscientiously    :    any  other  language,  for  that  matter,  wliirli  equals,   mneh   less  excels,  .KeynoMV  System. 

performed,  and  his  judicious  notes  distributed  tbroui:boul,  afford  abundant  evidence  of  the  Each  volume  contains  a  complete  index,  a  feature  which  tbns.-  \vho  may  have  encyclopaedic 

thoroughness  of  the  revision  at  his  hands.    In  conclusion,  we  take  pleasure  ID  commending  works  of   medicine   not  containing  this   index  can    fully   appre  'Kite.— .!//•<•.'/ I>IH   Metlirnl 

this  work  to  our  readers,  feeling  confident  that  it  will  not  only  become  t'aniliinl,  but  from  Xtin,  June  10,  1880. 

its  containing  just  th:it  information  which  the  busy  practitioner  t'requently  finds  himself  in  \Ve  regard  this  the  tinest  work  on  the  practice  of  medicine  iu  the  Kn-lisb  language.     In 

need  of,  from  its  completeness,  its  fulness  of  detail, .and  its  excellence,  it  will  >>  •  justly  up-  fact,  we  do  not  think  it  lias  its  superior  in  any  lannna^e  in  the  world.    Combining,  as  it 

predated  by  the  entire  profession  on  this  continent.— Kml/tern  J'rnrllliuner,  April,  Issu.  does,  a  c  miplete  history  ofdla  aaes,  a  thorough  account  of  their  patliolo-y.  a  lull  di'*eripii»n 

For  conciseness-  and  comprehensiveness  in  the  treatment  of  all  the  subjects  embraced  of  therapeutics,  and  a  minute  detail  of  treatment,  etc.,  it  embodies  all  that  a  practitioner 

under  the  head  of  "Practice  of  Medicine,"  there  is  no  work  in  the  English  language,  or  in  can  wish. — Ciix-iunni!  .V>v//,w/  7V//;<,<,  August  1880. 


HOLMES'    SYSTEM    OF    SURGERY.      Americanized.    Just  Ready. 

A  SYSTEM  OF  SURGERY,  THEORETICAL  AND  PRACTICAL.  In  Treatises  by  Various  Authors.  Edited  by  TIMOTHY 
HOLMES,  M.A.,  Surgeon  and  Lecturer  on  Surgery  at  St.  George's  Hospital,  London.  American  edition,  thoroughly  revised 
and  much  enlarged,  by  JOHN  H.  PACKARD,  M.  D.,  Surgeon  to  the  Episcopal  and  St.  Joseph's  Hospitals,  Philadelphia,  assisted 
by  a  corps  of  thirty-three  of  the  most  eminent  surgeons  of  America.  In  three  large  and  very  handsome  royal  octavo  volumes 
containing  3137  double-columned  pages,  with  979  illustrations  on  wood,  and  13  lithographic  plates,  beautifully  colored.  Per 
volume,  cloth,  $6;  leather,  $7;  half  Russia,  raised  bands,  $7.50.  Per  set,  cloth,  $18;  leather,  $21 ;  half  Russia,  raised  bands.  522.50. 

Representing  originally  the  most  advanced  school  of  British  surgery,  it  has  been  supple-  sufficient  guarantee  that  the  work  has  not  only  been  brought  fully  up  to  date,  but  aKo  iliai 

meuted,  through  the  labors  of  its  editor,  by  what  is  latest  and  best  in  the  surgery  of  America.  it  lias  been  accomplished  in  this  large,  thorough  and  scientific  spirit,  which  cbaracteri/es 

It  may  therefore  be  regarded  as  embodying  whatever  is  of  established  value  in  this  depart-  the  contributions  to  the  original  edition.— Canada  .Imntnl  of  .Mnlii-nl  .sv/?nc<<,  Nov.  ISM. 
ment  of  our  art.    No  surgeon  who  proposes  to  keep  abreast  with  bis  rivals  can  afford  to  be  The  elegant  American  revision  of  this  justly  celebrated  work,  wrill  give  to  the  American 

without  it.— Ainerii-on  Praetilioner,  April,  1882.  practitioners,  a  corresponding  collaboration  of  surgical  lore,  to  that  they  already  have  in 

It  is  a  subject  for  congratulation  that  the  idea  of  an  American  edition,  incorporating  possessing  the  volumes  of  Reynold.-.'  System  of  Medicine,  and  with  the  two  works,   the 


all  recently  acquired  knowledge  and  experience,  should  have  been  conceived    and    its 
execution  entrusted  to  such  able  hands  as  Packard's.    The  names  of  coadjutors  atlbrcl  a 


fortunate   possessor  has  a   most   complete  library  on   Practical   Medicine  and  Surgerv. — 

Brai(htrtiil<'K  I!<",/>,-;petl  and  Quai't> .<•///  /•.}'/>'""<''  •;'"  J'f<i<-/.    V"/.  "//'/  >'/</••/..  Sept.  ISsl. 


PERIODICALS. 


SUBSCRIPTION    RATES,    POSTAGE    PAID. 

THE  MEDICAL  NEWS  (published  every  Saturday)  in  advance SS-oo 

THE  AMERICAN  JOURNAL  OF  THE  MEDICAL  SCIENCBS  (quarterly)  in  advance 55.00 

COMMUTATION    RATES. 

TIIK  MEDICAL  NEWS %  . 

THE  AMERICAS  JOURNAL  OK  THE  MEDICAL  SCIKSCKS /  " 

THE   AMERICAN   JOURNAL   OF  THE   MEDICAL   SCIENCES. 

I.    MINIS   HAYS,    A.  M.,  M.  D.,    EDITOR. 


For  sixty-two  years  the  AMERICAN  JOURNAL  has  maintained  its  position  in  the  front  rank  of  medical  literature,  and  to-day  it  stands  alone  as  the  only  periodical 
in  the  English  language  capable  of  presenting  extended  and  elaborate  articles  on  every  branch  of  medical  science,  the  very  class  of  contributions,  in  fact,  in  which 
nearly  all  the  important  discoveries  in  the  science  have  been  communicated  to  the  profession. 

During  the  year  the  JOURNAL  will  present,  in  its  ORIGINAL  DEPARTMENT,  a  continuation  of  elaborate  articles  from  the  pens  of  the  most  eminent  members  of 
the  profession  throughout  the  country.  The  REVIEW  DEPARTMENT  will  contain  extended  reviews  of  prominent  new  works,  by  competent  writers,  together  with 
numerous  analytical  and  bibliographical  notices,  giving  a  full  survey  of  medical  literature.  The  QUARTERLY  SUMMARY  OF  IMPROVEMENTS  AND  DISCOVERIES  IN  THE 
MEDICAL  SCIENCES,  classified  and  arranged  under  various  heads,  will  furnish  a  digest  of  medical  progress  at  home  and  abroad. 

With  the  issue  for  January,  1882,  the  size  of  the  JOURNAL  was  permanently  increased  by  the  addition  of  16  to  20  pages.  It  is  still  furnished,  free  of  postage, 
for  FIVE  DOLLARS  per  annum,  in  advance.  

THE    MEDICAL    NEWS. 

A  NATIONAL  WEEKLY  MEDICAL  PERIODICAL,  PUBLISHED  EVERY  SATURDAY,  EACH  NUMBER  CONTAINING 
28  DOUBLE-COLUMNED  QUARTO  PAGES,  EXCLUSIVE  OF  ADVERTISEMENTS. 


The  MEDICAL  NEWS  aims  to  satisfy  the  demand  of  the  profession  for  the  most  rapid  possible  conveyance  of  intelligence,  in  short,  to  be  a  professional  ne\\s 
paper.  To  this  end  it  comprises  the  following  departments:  1st.  CLINICAL  I.K<  ITKES,  by  the  ablest  teachers  of  the  day.  2nd.  ORIGINAL  ARTICLES,  of  a  brief  and 
practical  nature.  3rd.  HOSPITAL  NOTES,  gleaned  from  the  leading  hospitals  on  both  continents.  4th.  The  PROGRESS  OF  MEDICAL  SCIENCE,  being  extracts  from  the 
medical  and  scientific  journals  in  all  quarters  of  the  globe,  showing  the  advances  made  in  medicine.  5th.  The  EDITORIAL  DEPARTMENT,  conducted  by  a  large  and 
able  Editorial  Staff.  6th.  PROCEEDINGS  of  the  meetings  of  prominent  medical  societies.  7th.  NEWS  ITEMS  AND  CORRESPONDENCE  from  the  pens  of  medical  men  in 
the  leading  cities  of  the  United  States,  Canada,  Great  Britain,  the  Continent  of  Europe,  Asia,  South  America  and  Cuba.  8th.  NOTICES  of  new  publications,  new 
instruments,  and  new  pharmaceutical  preparations,  and  a  column  of  NOTES  AND  QUERIES.  A  feature  characteristic  of  the  NEWS  will  be  a  liberal  use  of  the 
telegraph.  The  NEWS  is  printed  by  the  finest  Hoe  presses,  on  handsome  paper,  from  beautiful  type  cast  expressly  for  its  use.  The  price,  FIVE  DOLLARS  a  year. 
in  advance,  places  it  within  the  means  of  every  physician  to  subscribe  to  a  medical  newspaper,  which  represents  the  most  enlightened  thought,  and  possesses  the  most 
progressive  spirit  of  the  age. 

THE  AMERICAN  JOURNAL  and  the  MEDICAL  NEWS  together  contain  an  amount  of  the  choicest  medical  literature  equal  to  4000  large  octavo  pages,  in  \,'iich 
duplication  of  matter  is  prevented  by  special  arrangement.  They  will  be  furnished  for  NINE  DOLLARS  per  annum,  in  advance,  an  offer  unparalleled  in  the 
history  of  medical  journalism. 


mm:m 

fcj>*'fe  j\/  wHT" 

sPiSr^    y^su?    -JStf- 


&%JsfeTW 


miS^SBK 

5&&uP    ?32*^  3?  ^ 

^&       % 


lH 


^%MM 

igKf^-sra**" 

»TUCr  ^?s 


^^yErOT 

^ft 


m: 


$j?  •* j%  '~T^^J^*^  4^»yp^ 

^^®®^S3B«; 

^s^^^  H  i^a?.  >•          rlfife  ^-^^  mtf 


^'^^i 

^^JfZSBMS 

^ 

•tR'faSy^.^Fj^'aei. 


yffiM&Eim 


